code: # Copyright 2015 The TensorFlow Authors. All Rights Reserved.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  # ==============================================================================
  """Classes and functions used to construct graphs."""
  # pylint: disable=g-bad-name
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  import collections
  import re
  import sys
  import threading
  import types
  
  import numpy as np
  import six
  from six.moves import map  # pylint: disable=redefined-builtin
  from six.moves import xrange  # pylint: disable=redefined-builtin
  
  from tensorflow.core.framework import attr_value_pb2
  from tensorflow.core.framework import function_pb2
  from tensorflow.core.framework import graph_pb2
  from tensorflow.core.framework import node_def_pb2
  from tensorflow.core.framework import op_def_pb2
  from tensorflow.core.framework import versions_pb2
  from tensorflow.core.protobuf import config_pb2
  # pywrap_tensorflow must be imported first to avoid profobuf issues.
  # (b/143110113)
  # pylint: disable=invalid-import-order,g-bad-import-order,unused-import
  from tensorflow.python import pywrap_tensorflow
  from tensorflow.python import pywrap_tfe
  # pylint: enable=invalid-import-order,g-bad-import-order,unused-import
  from tensorflow.python import tf2
  from tensorflow.python.client import pywrap_tf_session
  from tensorflow.python.eager import context
  from tensorflow.python.eager import core
  from tensorflow.python.eager import monitoring
  from tensorflow.python.eager import tape
  from tensorflow.python.framework import c_api_util
  from tensorflow.python.framework import composite_tensor
  from tensorflow.python.framework import device as pydev
  from tensorflow.python.framework import dtypes
  from tensorflow.python.framework import errors
  from tensorflow.python.framework import indexed_slices
  from tensorflow.python.framework import registry
  from tensorflow.python.framework import tensor_conversion_registry
  from tensorflow.python.framework import tensor_like
  from tensorflow.python.framework import tensor_shape
  from tensorflow.python.framework import traceable_stack
  from tensorflow.python.framework import versions
  from tensorflow.python.ops import control_flow_util
  from tensorflow.python.platform import app
  from tensorflow.python.platform import tf_logging as logging
  from tensorflow.python.util import compat
  from tensorflow.python.util import decorator_utils
  from tensorflow.python.util import deprecation
  from tensorflow.python.util import function_utils
  from tensorflow.python.util import lock_util
  from tensorflow.python.util import memory
  from tensorflow.python.util import object_identity
  from tensorflow.python.util import tf_contextlib
  from tensorflow.python.util import tf_stack
  from tensorflow.python.util.compat import collections_abc
  from tensorflow.python.util.deprecation import deprecated_args
  from tensorflow.python.util.lazy_loader import LazyLoader
  from tensorflow.python.util.tf_export import kwarg_only
  from tensorflow.python.util.tf_export import tf_export
  
  ag_ctx = LazyLoader(
      "ag_ctx", globals(),
      "tensorflow.python.autograph.core.ag_ctx")
  
  
  # Temporary global switches determining if we should enable the work-in-progress
  # calls to the C API. These will be removed once all functionality is supported.
  _USE_C_API = True
  _USE_C_SHAPES = True
  
  _api_usage_gauge = monitoring.BoolGauge(
      "/tensorflow/api/ops_eager_execution",
      "Whether ops.enable_eager_execution() is called.")
  
  
  # pylint: disable=protected-access
  _TensorLike = tensor_like._TensorLike
  _DTYPES_INTERN_TABLE = dtypes._INTERN_TABLE
  # pylint: enable=protected-access
  
  
  def tensor_id(tensor):
    """Returns a unique identifier for this Tensor."""
    return tensor._id  # pylint: disable=protected-access
  
  
  class _UserDeviceSpec(object):
    """Store user-specified device and provide computation of merged device."""
  
    def __init__(self, device_name_or_function):
      self._device_name_or_function = device_name_or_function
      self.display_name = str(self._device_name_or_function)
      self.function = device_name_or_function
      self.raw_string = None
  
      if isinstance(device_name_or_function, pydev.MergeDevice):
        self.is_null_merge = device_name_or_function.is_null_merge
  
      elif callable(device_name_or_function):
        self.is_null_merge = False
        dev_func = self._device_name_or_function
        func_name = function_utils.get_func_name(dev_func)
        func_code = function_utils.get_func_code(dev_func)
        if func_code:
          fname = func_code.co_filename
          lineno = func_code.co_firstlineno
        else:
          fname = "unknown"
          lineno = -1
        self.display_name = "%s<%s, %d>" % (func_name, fname, lineno)
  
      elif device_name_or_function is None:
        # NOTE(taylorrobie): This MUST be False. None signals a break in the
        #   device stack, so `is_null_merge` must be False for such a case to
        #   allow callers to safely skip over null merges without missing a None.
        self.is_null_merge = False
  
      else:
        self.raw_string = device_name_or_function
        self.function = pydev.merge_device(device_name_or_function)
        self.is_null_merge = self.function.is_null_merge
  
      # We perform this check in __init__ because it is of non-trivial cost,
      # and self.string_merge is typically called many times.
      self.fast_string_merge = isinstance(self.function, pydev.MergeDevice)
  
    def string_merge(self, node_def):
      if self.fast_string_merge:
        return self.function.shortcut_string_merge(node_def)
  
      return compat.as_str(_device_string(self.function(node_def)))
  
  
  class NullContextmanager(object):
  
    def __init__(self, *args, **kwargs):
      pass
  
    def __enter__(self):
      pass
  
    def __exit__(self, type_arg, value_arg, traceback_arg):
      return False  # False values do not suppress exceptions
  
  
  def _override_helper(clazz_object, operator, func):
    """Overrides (string) operator on Tensors to call func.
  
    Args:
      clazz_object: the class to override for; either Tensor or SparseTensor.
      operator: the string name of the operator to override.
      func: the function that replaces the overridden operator.
  
    Raises:
      ValueError: If operator has already been overwritten,
        or if operator is not allowed to be overwritten.
    """
    existing = getattr(clazz_object, operator, None)
    if existing is not None:
      # Check to see if this is a default method-wrapper or slot wrapper which
      # will be true for the comparison operators.
      if not isinstance(existing, type(object.__lt__)):
        raise ValueError("operator %s cannot be overwritten again on class %s." %
                         (operator, clazz_object))
    if operator not in Tensor.OVERLOADABLE_OPERATORS:
      raise ValueError("Overriding %s is disallowed" % operator)
    setattr(clazz_object, operator, func)
  
  
  def _as_graph_element(obj):
    """Convert `obj` to a graph element if possible, otherwise return `None`.
  
    Args:
      obj: Object to convert.
  
    Returns:
      The result of `obj._as_graph_element()` if that method is available;
          otherwise `None`.
    """
    conv_fn = getattr(obj, "_as_graph_element", None)
    if conv_fn and callable(conv_fn):
      return conv_fn()
    return None
  
  
  _TENSOR_LIKE_TYPES = tuple()
  
  
  def is_dense_tensor_like(t):
    """EXPERIMENTAL: Returns true if `t` implements the tensor interface.
  
    See `register_dense_tensor_like_type()` for the current definition of a
    "tensor-like type".
  
    Args:
      t: An object.
  
    Returns:
      True iff `t` is an instance of one of the registered "tensor-like" types.
    """
    return isinstance(t, _TENSOR_LIKE_TYPES)
  
  
  def register_dense_tensor_like_type(tensor_type):
    """EXPERIMENTAL: Registers `tensor_type` as implementing the tensor interface.
  
    A "tensor-like type" can represent a single dense tensor, and implements
    the `name`, `dtype` and `shape` properties.
  
    Args:
      tensor_type: A type implementing the tensor interface.
  
    Raises:
      TypeError: If `tensor_type` does not implement the tensor interface.
    """
    if not (hasattr(tensor_type, "name") and
            isinstance(tensor_type.name, property)):
      raise TypeError("Type %s does not define a `name` property" %
                      tensor_type.__name__)
    if not (hasattr(tensor_type, "dtype") and
            isinstance(tensor_type.dtype, property)):
      raise TypeError("Type %s does not define a `dtype` property" %
                      tensor_type.__name__)
    if not (hasattr(tensor_type, "shape") and
            isinstance(tensor_type.shape, property)):
      raise TypeError("Type %s does not define a `shape` property" %
                      tensor_type.__name__)
    # We expect this list to be small, so choose quadratic complexity
    # for registration, so that we have a tuple that can be used for
    # more efficient `isinstance` checks later.
    global _TENSOR_LIKE_TYPES
    _TENSOR_LIKE_TYPES = tuple(list(_TENSOR_LIKE_TYPES) + [tensor_type])
  
  
  def uid():
    """A unique (within this program execution) integer."""
    return pywrap_tfe.TFE_Py_UID()
  
  
  def numpy_text(tensor, is_repr=False):
    """Human readable representation of a tensor's numpy value."""
    if tensor.dtype.is_numpy_compatible:
      # pylint: disable=protected-access
      text = repr(tensor._numpy()) if is_repr else str(tensor._numpy())
      # pylint: enable=protected-access
    else:
      text = "<unprintable>"
    if "\n" in text:
      text = "\n" + text
    return text
  
  @tf_export(v1=["enable_tensor_equality"])
  def enable_tensor_equality():
    """Compare Tensors with element-wise comparison and thus be unhashable.
  
    Comparing tensors with element-wise allows comparisons such as
    tf.Variable(1.0) == 1.0. Element-wise equality implies that tensors are
    unhashable. Thus tensors can no longer be directly used in sets or as a key in
    a dictionary.
    """
    Tensor._USE_EQUALITY = True  # pylint: disable=protected-access
  
  @tf_export(v1=["disable_tensor_equality"])
  def disable_tensor_equality():
    """Compare Tensors by their id and be hashable.
  
    This is a legacy behaviour of TensorFlow and is highly discouraged.
    """
    Tensor._USE_EQUALITY = False  # pylint: disable=protected-access
  
  
  @tf_export("Tensor")
  class Tensor(_TensorLike):
    """A tensor represents a rectangular array of data.
  
    When writing a TensorFlow program, the main object you manipulate and pass
    around is the `tf.Tensor`. A `tf.Tensor` object represents a rectangular array
    of arbitrary dimension, filled with data of a specific data type.
  
    A `tf.Tensor` has the following properties:
  
    * a data type (float32, int32, or string, for example)
    * a shape
  
    Each element in the Tensor has the same data type, and the data type is always
    known.
  
    In eager execution, which is the default mode in TensorFlow, results are
    calculated immediately.
  
    >>> # Compute some values using a Tensor
    >>> c = tf.constant([[1.0, 2.0], [3.0, 4.0]])
    >>> d = tf.constant([[1.0, 1.0], [0.0, 1.0]])
    >>> e = tf.matmul(c, d)
    >>> print(e)
    tf.Tensor(
    [[1. 3.]
     [3. 7.]], shape=(2, 2), dtype=float32)
  
  
    Note that during eager execution, you may discover your `Tensors` are actually
    of type `EagerTensor`.  This is an internal detail, but it does give you
    access to a useful function, `numpy`:
  
    >>> type(e)
    <class '...ops.EagerTensor'>
    >>> print(e.numpy())
      [[1. 3.]
       [3. 7.]]
  
    TensorFlow can define computations without immediately executing them, most
    commonly inside `tf.function`s, as well as in (legacy) Graph mode. In those
    cases, the shape (that is, the rank of the Tensor and the size of
    each dimension) might be only partially known.
  
    Most operations produce tensors of fully-known shapes if the shapes of their
    inputs are also fully known, but in some cases it's only possible to find the
    shape of a tensor at execution time.
  
    There are specialized tensors; for these, see `tf.Variable`, `tf.constant`,
    `tf.placeholder`, `tf.SparseTensor`, and `tf.RaggedTensor`.
  
    For more on Tensors, see the [guide](https://tensorflow.org/guide/tensor`).
    """
  
    # List of Python operators that we allow to override.
    OVERLOADABLE_OPERATORS = {
        # Binary.
        "__add__",
        "__radd__",
        "__sub__",
        "__rsub__",
        "__mul__",
        "__rmul__",
        "__div__",
        "__rdiv__",
        "__truediv__",
        "__rtruediv__",
        "__floordiv__",
        "__rfloordiv__",
        "__mod__",
        "__rmod__",
        "__lt__",
        "__le__",
        "__gt__",
        "__ge__",
        "__ne__",
        "__eq__",
        "__and__",
        "__rand__",
        "__or__",
        "__ror__",
        "__xor__",
        "__rxor__",
        "__getitem__",
        "__pow__",
        "__rpow__",
        # Unary.
        "__invert__",
        "__neg__",
        "__abs__",
        "__matmul__",
        "__rmatmul__"
    }
  
    # Whether to allow hashing or numpy-style equality
    _USE_EQUALITY = tf2.enabled()
  
    def __init__(self, op, value_index, dtype):
      """Creates a new `Tensor`.
  
      Args:
        op: An `Operation`. `Operation` that computes this tensor.
        value_index: An `int`. Index of the operation's endpoint that produces
          this tensor.
        dtype: A `DType`. Type of elements stored in this tensor.
  
      Raises:
        TypeError: If the op is not an `Operation`.
      """
      if not isinstance(op, Operation):
        raise TypeError("op needs to be an Operation: %s" % op)
      self._op = op
      self._value_index = value_index
      self._dtype = dtypes.as_dtype(dtype)
      # This will be set by self._as_tf_output().
      self._tf_output = None
      # This will be set by self.shape().
      self._shape_val = None
      # List of operations that use this Tensor as input.  We maintain this list
      # to easily navigate a computation graph.
      self._consumers = []
      self._id = uid()
      self._name = None
  
    @staticmethod
    def _create_with_tf_output(op, value_index, dtype, tf_output):
      ret = Tensor(op, value_index, dtype)
      ret._tf_output = tf_output
      return ret
  
    @property
    def op(self):
      """The `Operation` that produces this tensor as an output."""
      return self._op
  
    @property
    def dtype(self):
      """The `DType` of elements in this tensor."""
      return self._dtype
  
    @property
    def graph(self):
      """The `Graph` that contains this tensor."""
      return self._op.graph
  
    @property
    def name(self):
      """The string name of this tensor."""
      if self._name is None:
        if not self._op.name:
          raise ValueError("Operation was not named: %s" % self._op)
        self._name = "%s:%d" % (self._op.name, self._value_index)
      return self._name
  
    @property
    def device(self):
      """The name of the device on which this tensor will be produced, or None."""
      return self._op.device
  
    @property
    def shape(self):
      """Returns the `TensorShape` that represents the shape of this tensor.
  
      The shape is computed using shape inference functions that are
      registered in the Op for each `Operation`.  See
      `tf.TensorShape`
      for more details of what a shape represents.
  
      The inferred shape of a tensor is used to provide shape
      information without having to execute the underlying kernel. This
      can be used for debugging and providing early error messages. For
      example:
  
      ```python
      >>> c = tf.constant([[1.0, 2.0, 3.0], [4.0, 5.0, 6.0]])
      >>> print(c.shape) # will be TensorShape([2, 3])
      (2, 3)
  
      >>> d = tf.constant([[1.0, 0.0], [0.0, 1.0], [1.0, 0.0], [0.0, 1.0]])
      >>> print(d.shape)
      (4, 2)
  
      # Raises a ValueError, because `c` and `d` do not have compatible
      # inner dimensions.
      >>> e = tf.matmul(c, d)
      Traceback (most recent call last):
          ...
      tensorflow.python.framework.errors_impl.InvalidArgumentError: Matrix
      size-incompatible: In[0]: [2,3], In[1]: [4,2] [Op:MatMul] name: MatMul/
  
      # This works because we have compatible shapes.
      >>> f = tf.matmul(c, d, transpose_a=True, transpose_b=True)
      >>> print(f.shape)
      (3, 4)
  
      ```
  
      In some cases, the inferred shape may have unknown dimensions. If
      the caller has additional information about the values of these
      dimensions, `Tensor.set_shape()` can be used to augment the
      inferred shape.
  
      Returns:
        A `tf.TensorShape` representing the shape of this tensor.
  
      """
      if self._shape_val is None:
        self._shape_val = self._c_api_shape()
      return self._shape_val
  
    def _c_api_shape(self):
      """Returns the TensorShape of this tensor according to the C API."""
      c_graph = self._op._graph._c_graph  # pylint: disable=protected-access
      shape_vec, unknown_shape = pywrap_tf_session.TF_GraphGetTensorShapeHelper(
          c_graph, self._as_tf_output())
      if unknown_shape:
        return tensor_shape.unknown_shape()
      else:
        shape_vec = [None if d == -1 else d for d in shape_vec]
        return tensor_shape.TensorShape(shape_vec)
  
    @property
    def _shape(self):
      logging.warning("Tensor._shape is private, use Tensor.shape "
                      "instead. Tensor._shape will eventually be removed.")
      return self.shape
  
    @_shape.setter
    def _shape(self, value):
      raise ValueError(
          "Tensor._shape cannot be assigned, use Tensor.set_shape instead.")
  
    def _disallow_when_autograph_disabled(self, task):
      raise errors.OperatorNotAllowedInGraphError(
          "{} is not allowed: AutoGraph is disabled in this function."
          " Try decorating it directly with @tf.function.".format(task))
  
    def _disallow_when_autograph_enabled(self, task):
      raise errors.OperatorNotAllowedInGraphError(
          "{} is not allowed: AutoGraph did not convert this function. Try"
          " decorating it directly with @tf.function.".format(task))
  
    def _disallow_in_graph_mode(self, task):
      raise errors.OperatorNotAllowedInGraphError(
          "{} is not allowed in Graph execution. Use Eager execution or decorate"
          " this function with @tf.function.".format(task))
  
    def _disallow_bool_casting(self):
      if ag_ctx.control_status_ctx().status == ag_ctx.Status.DISABLED:
        self._disallow_when_autograph_disabled(
            "using a `tf.Tensor` as a Python `bool`")
      elif ag_ctx.control_status_ctx().status == ag_ctx.Status.ENABLED:
        self._disallow_when_autograph_enabled(
            "using a `tf.Tensor` as a Python `bool`")
      else:
        # Default: V1-style Graph execution.
        self._disallow_in_graph_mode("using a `tf.Tensor` as a Python `bool`")
  
    def _disallow_iteration(self):
      if ag_ctx.control_status_ctx().status == ag_ctx.Status.DISABLED:
        self._disallow_when_autograph_disabled("iterating over `tf.Tensor`")
      elif ag_ctx.control_status_ctx().status == ag_ctx.Status.ENABLED:
        self._disallow_when_autograph_enabled("iterating over `tf.Tensor`")
      else:
        # Default: V1-style Graph execution.
        self._disallow_in_graph_mode("iterating over `tf.Tensor`")
  
    def __iter__(self):
      if not context.executing_eagerly():
        self._disallow_iteration()
  
      shape = self._shape_tuple()
      if shape is None:
        raise TypeError("Cannot iterate over a tensor with unknown shape.")
      if not shape:
        raise TypeError("Cannot iterate over a scalar tensor.")
      if shape[0] is None:
        raise TypeError(
            "Cannot iterate over a tensor with unknown first dimension.")
      return _TensorIterator(self, shape[0])
  
    def _shape_as_list(self):
      if self.shape.ndims is not None:
        return [dim.value for dim in self.shape.dims]
      else:
        return None
  
    def _shape_tuple(self):
      shape = self._shape_as_list()
      if shape is None:
        return None
      return tuple(shape)
  
    def _rank(self):
      """Integer rank of this Tensor, if known, else None.
  
      Returns:
        Integer rank or None
      """
      return self.shape.ndims
  
    def get_shape(self):
      """Alias of `tf.Tensor.shape`."""
      return self.shape
  
    def set_shape(self, shape):
      """Updates the shape of this tensor.
  
      This method can be called multiple times, and will merge the given
      `shape` with the current shape of this tensor. It can be used to
      provide additional information about the shape of this tensor that
      cannot be inferred from the graph alone. For example, this can be used
      to provide additional information about the shapes of images:
  
      ```python
      _, image_data = tf.compat.v1.TFRecordReader(...).read(...)
      image = tf.image.decode_png(image_data, channels=3)
  
      # The height and width dimensions of `image` are data dependent, and
      # cannot be computed without executing the op.
      print(image.shape)
      ==> TensorShape([Dimension(None), Dimension(None), Dimension(3)])
  
      # We know that each image in this dataset is 28 x 28 pixels.
      image.set_shape([28, 28, 3])
      print(image.shape)
      ==> TensorShape([Dimension(28), Dimension(28), Dimension(3)])
      ```
  
      NOTE: This shape is not enforced at runtime. Setting incorrect shapes can
      result in inconsistencies between the statically-known graph and the runtime
      value of tensors. For runtime validation of the shape, use `tf.ensure_shape`
      instead.
  
      Args:
        shape: A `TensorShape` representing the shape of this tensor, a
          `TensorShapeProto`, a list, a tuple, or None.
  
      Raises:
        ValueError: If `shape` is not compatible with the current shape of
          this tensor.
      """
      # Reset cached shape.
      self._shape_val = None
  
      # We want set_shape to be reflected in the C API graph for when we run it.
      if not isinstance(shape, tensor_shape.TensorShape):
        shape = tensor_shape.TensorShape(shape)
      dim_list = []
      if shape.dims is None:
        unknown_shape = True
      else:
        unknown_shape = False
        for dim in shape.dims:
          if dim.value is None:
            dim_list.append(-1)
          else:
            dim_list.append(dim.value)
      try:
        pywrap_tf_session.TF_GraphSetTensorShape_wrapper(
            self._op._graph._c_graph,  # pylint: disable=protected-access
            self._as_tf_output(),
            dim_list,
            unknown_shape)
      except errors.InvalidArgumentError as e:
        # Convert to ValueError for backwards compatibility.
        raise ValueError(str(e))
  
    @property
    def value_index(self):
      """The index of this tensor in the outputs of its `Operation`."""
      return self._value_index
  
    def consumers(self):
      """Returns a list of `Operation`s that consume this tensor.
  
      Returns:
        A list of `Operation`s.
      """
      consumer_names = pywrap_tf_session.TF_OperationOutputConsumers_wrapper(
          self._as_tf_output())
      # pylint: disable=protected-access
      return [
          self.graph._get_operation_by_name_unsafe(name)
          for name in consumer_names
      ]
      # pylint: enable=protected-access
  
    def _as_node_def_input(self):
      """Return a value to use for the NodeDef "input" attribute.
  
      The returned string can be used in a NodeDef "input" attribute
      to indicate that the NodeDef uses this Tensor as input.
  
      Raises:
        ValueError: if this Tensor's Operation does not have a name.
  
      Returns:
        a string.
      """
      if not self._op.name:
        raise ValueError("Operation was not named: %s" % self._op)
      if self._value_index == 0:
        return self._op.name
      else:
        return "%s:%d" % (self._op.name, self._value_index)
  
    def _as_tf_output(self):
      # pylint: disable=protected-access
      # NOTE: Beyond preventing unnecessary (re-)allocation, the cached object
      # also guarantees that a dictionary of tf_output objects will retain a
      # deterministic (yet unsorted) order which prevents memory blowup in the
      # cache of executor(s) stored for every session.
      if self._tf_output is None:
        self._tf_output = c_api_util.tf_output(self.op._c_op, self.value_index)
      return self._tf_output
      # pylint: enable=protected-access
  
    def __str__(self):
      return "Tensor(\"%s\"%s%s%s)" % (
          self.name,
          (", shape=%s" %
           self.get_shape()) if self.get_shape().ndims is not None else "",
          (", dtype=%s" % self._dtype.name) if self._dtype else "",
          (", device=%s" % self.device) if self.device else "")
  
    def __repr__(self):
      return "<tf.Tensor '%s' shape=%s dtype=%s>" % (self.name, self.get_shape(),
                                                     self._dtype.name)
  
    def __hash__(self):
      g = getattr(self, "graph", None)
      if (Tensor._USE_EQUALITY and executing_eagerly_outside_functions() and
          (g is None or g.building_function)):
        raise TypeError("Tensor is unhashable. "
                        "Instead, use tensor.ref() as the key.")
      else:
        return id(self)
  
    def __copy__(self):
      # TODO(b/77597810): get rid of Tensor copies.
      cls = self.__class__
      result = cls.__new__(cls)
      result.__dict__.update(self.__dict__)
      return result
  
    # NOTE(mrry): This enables the Tensor's overloaded "right" binary
    # operators to run when the left operand is an ndarray, because it
    # accords the Tensor class higher priority than an ndarray, or a
    # numpy matrix.
    # TODO(mrry): Convert this to using numpy's __numpy_ufunc__
    # mechanism, which allows more control over how Tensors interact
    # with ndarrays.
    __array_priority__ = 100
  
    def __array__(self):
      raise NotImplementedError("Cannot convert a symbolic Tensor ({}) to a numpy"
                                " array.".format(self.name))
  
    def __len__(self):
      raise TypeError("len is not well defined for symbolic Tensors. ({}) "
                      "Please call `x.shape` rather than `len(x)` for "
                      "shape information.".format(self.name))
  
    @staticmethod
    def _override_operator(operator, func):
      _override_helper(Tensor, operator, func)
  
    def __bool__(self):
      """Dummy method to prevent a tensor from being used as a Python `bool`.
  
      This overload raises a `TypeError` when the user inadvertently
      treats a `Tensor` as a boolean (most commonly in an `if` or `while`
      statement), in code that was not converted by AutoGraph. For example:
  
      ```python
      if tf.constant(True):  # Will raise.
        # ...
  
      if tf.constant(5) < tf.constant(7):  # Will raise.
        # ...
      ```
  
      Raises:
        `TypeError`.
      """
      self._disallow_bool_casting()
  
    def __nonzero__(self):
      """Dummy method to prevent a tensor from being used as a Python `bool`.
  
      This is the Python 2.x counterpart to `__bool__()` above.
  
      Raises:
        `TypeError`.
      """
      self._disallow_bool_casting()
  
    def eval(self, feed_dict=None, session=None):
      """Evaluates this tensor in a `Session`.
  
      Note: If you are not using `compat.v1` libraries, you should not need this,
      (or `feed_dict` or `Session`).  In eager execution (or within `tf.function`)
      you do not need to call `eval`.
  
      Calling this method will execute all preceding operations that
      produce the inputs needed for the operation that produces this
      tensor.
  
      *N.B.* Before invoking `Tensor.eval()`, its graph must have been
      launched in a session, and either a default session must be
      available, or `session` must be specified explicitly.
  
      Args:
        feed_dict: A dictionary that maps `Tensor` objects to feed values. See
          `tf.Session.run` for a description of the valid feed values.
        session: (Optional.) The `Session` to be used to evaluate this tensor. If
          none, the default session will be used.
  
      Returns:
        A numpy array corresponding to the value of this tensor.
      """
      return _eval_using_default_session(self, feed_dict, self.graph, session)
  
    @deprecation.deprecated(None, "Use ref() instead.")
    def experimental_ref(self):
      return self.ref()
  
    def ref(self):
      # tf.Variable also has the same ref() API.  If you update the
      # documentation here, please update tf.Variable.ref() as well.
      """Returns a hashable reference object to this Tensor.
  
      The primary use case for this API is to put tensors in a set/dictionary.
      We can't put tensors in a set/dictionary as `tensor.__hash__()` is no longer
      available starting Tensorflow 2.0.
  
      The following will raise an exception starting 2.0
  
      >>> x = tf.constant(5)
      >>> y = tf.constant(10)
      >>> z = tf.constant(10)
      >>> tensor_set = {x, y, z}
      Traceback (most recent call last):
        ...
      TypeError: Tensor is unhashable. Instead, use tensor.ref() as the key.
      >>> tensor_dict = {x: 'five', y: 'ten'}
      Traceback (most recent call last):
        ...
      TypeError: Tensor is unhashable. Instead, use tensor.ref() as the key.
  
      Instead, we can use `tensor.ref()`.
  
      >>> tensor_set = {x.ref(), y.ref(), z.ref()}
      >>> x.ref() in tensor_set
      True
      >>> tensor_dict = {x.ref(): 'five', y.ref(): 'ten', z.ref(): 'ten'}
      >>> tensor_dict[y.ref()]
      'ten'
  
      Also, the reference object provides `.deref()` function that returns the
      original Tensor.
  
      >>> x = tf.constant(5)
      >>> x.ref().deref()
      <tf.Tensor: shape=(), dtype=int32, numpy=5>
      """
      return object_identity.Reference(self)
  
  
  # TODO(agarwal): consider getting rid of this.
  class _EagerTensorBase(Tensor):
    """Base class for EagerTensor."""
  
    # __complex__, __int__, __float__ and __index__ may copy the tensor to CPU and
    # only work for scalars; values are cast as per numpy.
    def __complex__(self):
      return complex(self._numpy())
  
    def __int__(self):
      return int(self._numpy())
  
    def __long__(self):
      return long(self._numpy())
  
    def __float__(self):
      return float(self._numpy())
  
    def __index__(self):
      return self._numpy().__index__()
  
    def __bool__(self):
      return bool(self._numpy())
  
    __nonzero__ = __bool__
  
    def __format__(self, format_spec):
      return self._numpy().__format__(format_spec)
  
    def __reduce__(self):
      return convert_to_tensor, (self._numpy(),)
  
    def __copy__(self):
      # Eager Tensors are immutable so it's safe to return themselves as a copy.
      return self
  
    def __deepcopy__(self, memo):
      # Eager Tensors are immutable so it's safe to return themselves as a copy.
      del memo
      return self
  
    def __str__(self):
      return "tf.Tensor(%s, shape=%s, dtype=%s)" % (numpy_text(self), self.shape,
                                                    self.dtype.name)
  
    def __repr__(self):
      return "<tf.Tensor: shape=%s, dtype=%s, numpy=%s>" % (
          self.shape, self.dtype.name, numpy_text(self, is_repr=True))
  
    def __len__(self):
      """Returns the length of the first dimension in the Tensor."""
      if not self.shape.ndims:
        raise TypeError("Scalar tensor has no `len()`")
      # pylint: disable=protected-access
      try:
        return self._shape_tuple()[0]
      except core._NotOkStatusException as e:
        six.raise_from(core._status_to_exception(e.code, e.message), None)
  
    def _numpy_internal(self):
      raise NotImplementedError()
  
    def _numpy(self):
      # pylint: disable=protected-access
      try:
        return self._numpy_internal()
      except core._NotOkStatusException as e:
        six.raise_from(core._status_to_exception(e.code, e.message), None)
  
    @property
    def dtype(self):
      # Note: using the intern table directly here as this is
      # performance-sensitive in some models.
      return dtypes._INTERN_TABLE[self._datatype_enum()]  # pylint: disable=protected-access
  
    def numpy(self):
      """Copy of the contents of this Tensor into a NumPy array or scalar.
  
      Unlike NumPy arrays, Tensors are immutable, so this method has to copy
      the contents to ensure safety. Use `memoryview` to get a readonly
      view of the contents without doing a copy:
  
      >>> t = tf.constant([42])
      >>> np.array(memoryview(t))
      array([42], dtype=int32)
  
      Note that `memoryview` is only zero-copy for Tensors on CPU. If a Tensor
      is on GPU, it will have to be transferred to CPU first in order for
      `memoryview` to work.
  
      Returns:
        A NumPy array of the same shape and dtype or a NumPy scalar, if this
        Tensor has rank 0.
  
      Raises:
        ValueError: If the dtype of this Tensor does not have a compatible
          NumPy dtype.
      """
      # TODO(slebedev): Consider avoiding a copy for non-CPU or remote tensors.
      maybe_arr = self._numpy()  # pylint: disable=protected-access
      return maybe_arr.copy() if isinstance(maybe_arr, np.ndarray) else maybe_arr
  
    @property
    def backing_device(self):
      """Returns the name of the device holding this tensor's memory.
  
      `.backing_device` is usually the same as `.device`, which returns
      the device on which the kernel of the operation that produced this tensor
      ran. However, some operations can produce tensors on a different device
      (e.g., an operation that executes on the GPU but produces output tensors
      in host memory).
      """
      raise NotImplementedError()
  
    def _datatype_enum(self):
      raise NotImplementedError()
  
    def _shape_tuple(self):
      """The shape of this Tensor, as a tuple.
  
      This is more performant than tuple(shape().as_list()) as it avoids
      two list and one object creation. Marked private for now as from an API
      perspective, it would be better to have a single performant way of
      getting a shape rather than exposing shape() and shape_tuple()
      (and heaven forbid, shape_list() etc. as well!). Punting on that for now,
      but ideally one would work things out and remove the need for this method.
  
      Returns:
        tuple with the shape.
      """
      raise NotImplementedError()
  
    def _rank(self):
      """Integer rank of this Tensor.
  
      Unlike regular Tensors, the rank is always known for EagerTensors.
  
      This is more performant than len(self._shape_tuple())
  
      Returns:
        Integer rank
      """
      raise NotImplementedError()
  
    def _num_elements(self):
      """Number of elements of this Tensor.
  
      Unlike regular Tensors, the number of elements is always known for
      EagerTensors.
  
      This is more performant than tensor.shape.num_elements
  
      Returns:
        Long - num elements in the tensor
      """
      raise NotImplementedError()
  
    def _copy_to_device(self, device_name):  # pylint: disable=redefined-outer-name
      raise NotImplementedError()
  
    @staticmethod
    def _override_operator(name, func):
      setattr(_EagerTensorBase, name, func)
  
    def _copy_nograd(self, ctx=None, device_name=None):
      """Copies tensor to dest device, but doesn't record the operation."""
      # Creates a new tensor on the dest device.
      if ctx is None:
        ctx = context.context()
      if device_name is None:
        device_name = ctx.device_name
      # pylint: disable=protected-access
      try:
        ctx.ensure_initialized()
        new_tensor = self._copy_to_device(device_name)
      except core._NotOkStatusException as e:
        six.raise_from(core._status_to_exception(e.code, e.message), None)
      return new_tensor
  
    def _copy(self, ctx=None, device_name=None):
      """Copies tensor to dest device."""
      new_tensor = self._copy_nograd(ctx, device_name)
      # Record the copy on tape and define backprop copy as well.
      if context.executing_eagerly():
        self_device = self.device
  
        def grad_fun(dresult):
          return [
              dresult._copy(device_name=self_device)
              if hasattr(dresult, "_copy") else dresult
          ]
  
        tape.record_operation("_copy", [new_tensor], [self], grad_fun)
      return new_tensor
      # pylint: enable=protected-access
  
    @property
    def shape(self):
      if self._tensor_shape is None:  # pylint: disable=access-member-before-definition
        # pylint: disable=protected-access
        try:
          # `_tensor_shape` is declared and defined in the definition of
          # `EagerTensor`, in C.
          self._tensor_shape = tensor_shape.TensorShape(self._shape_tuple())
        except core._NotOkStatusException as e:
          six.raise_from(core._status_to_exception(e.code, e.message), None)
  
      return self._tensor_shape
  
    def get_shape(self):
      """Alias of Tensor.shape."""
      return self.shape
  
    def _shape_as_list(self):
      """The shape of the tensor as a list."""
      return list(self._shape_tuple())
  
    @property
    def ndim(self):
      """Returns the number of Tensor dimensions."""
      return self.shape.ndims
  
    @deprecation.deprecated(None, "Use tf.identity instead.")
    def cpu(self):
      """A copy of this Tensor with contents backed by host memory."""
      return self._copy(context.context(), "CPU:0")
  
    @deprecation.deprecated(None, "Use tf.identity instead.")
    def gpu(self, gpu_index=0):
      """A copy of this Tensor with contents backed by memory on the GPU.
  
      Arguments:
        gpu_index: Identifies which GPU to place the contents on the returned
          Tensor in.
  
      Returns:
        A GPU-memory backed Tensor object initialized with the same contents
        as this Tensor.
      """
      return self._copy(context.context(), "GPU:" + str(gpu_index))
  
    def set_shape(self, shape):
      if not self.shape.is_compatible_with(shape):
        raise ValueError(
            "Tensor's shape %s is not compatible with supplied shape %s" %
            (self.shape, shape))
  
    # Methods not supported / implemented for Eager Tensors.
    @property
    def op(self):
      raise AttributeError(
          "Tensor.op is meaningless when eager execution is enabled.")
  
    @property
    def graph(self):
      raise AttributeError(
          "Tensor.graph is meaningless when eager execution is enabled.")
  
    @property
    def name(self):
      raise AttributeError(
          "Tensor.name is meaningless when eager execution is enabled.")
  
    @property
    def value_index(self):
      raise AttributeError(
          "Tensor.value_index is meaningless when eager execution is enabled.")
  
    def consumers(self):
      raise NotImplementedError(
          "Tensor.consumers is meaningless when eager execution is enabled.")
  
    def _add_consumer(self, consumer):
      raise NotImplementedError(
          "_add_consumer not supported when eager execution is enabled.")
  
    def _as_node_def_input(self):
      raise NotImplementedError(
          "_as_node_def_input not supported when eager execution is enabled.")
  
    def _as_tf_output(self):
      raise NotImplementedError(
          "_as_tf_output not supported when eager execution is enabled.")
  
    def eval(self, feed_dict=None, session=None):
      raise NotImplementedError(
          "eval is not supported when eager execution is enabled, "
          "is .numpy() what you're looking for?")
  
  
  # This call creates an EagerTensor class, as a subclass of _EagerTensorBase, and
  # registers it with the current module.
  EagerTensor = pywrap_tfe.TFE_Py_InitEagerTensor(_EagerTensorBase)
  
  
  register_dense_tensor_like_type(Tensor)
  
  
  @tf_export(v1=["convert_to_tensor"])
  def convert_to_tensor_v1(value,
                           dtype=None,
                           name=None,
                           preferred_dtype=None,
                           dtype_hint=None):
    """Converts the given `value` to a `Tensor`.
  
    This function converts Python objects of various types to `Tensor`
    objects. It accepts `Tensor` objects, numpy arrays, Python lists,
    and Python scalars. For example:
  
    ```python
    import numpy as np
  
    def my_func(arg):
      arg = tf.convert_to_tensor(arg, dtype=tf.float32)
      return tf.matmul(arg, arg) + arg
  
    # The following calls are equivalent.
    value_1 = my_func(tf.constant([[1.0, 2.0], [3.0, 4.0]]))
    value_2 = my_func([[1.0, 2.0], [3.0, 4.0]])
    value_3 = my_func(np.array([[1.0, 2.0], [3.0, 4.0]], dtype=np.float32))
    ```
  
    This function can be useful when composing a new operation in Python
    (such as `my_func` in the example above). All standard Python op
    constructors apply this function to each of their Tensor-valued
    inputs, which allows those ops to accept numpy arrays, Python lists,
    and scalars in addition to `Tensor` objects.
  
    Note: This function diverges from default Numpy behavior for `float` and
      `string` types when `None` is present in a Python list or scalar. Rather
      than silently converting `None` values, an error will be thrown.
  
    Args:
      value: An object whose type has a registered `Tensor` conversion function.
      dtype: Optional element type for the returned tensor. If missing, the type
        is inferred from the type of `value`.
      name: Optional name to use if a new `Tensor` is created.
      preferred_dtype: Optional element type for the returned tensor, used when
        dtype is None. In some cases, a caller may not have a dtype in mind when
        converting to a tensor, so preferred_dtype can be used as a soft
        preference.  If the conversion to `preferred_dtype` is not possible, this
        argument has no effect.
      dtype_hint: same meaning as preferred_dtype, and overrides it.
  
    Returns:
      A `Tensor` based on `value`.
  
    Raises:
      TypeError: If no conversion function is registered for `value` to `dtype`.
      RuntimeError: If a registered conversion function returns an invalid value.
      ValueError: If the `value` is a tensor not of given `dtype` in graph mode.
    """
    preferred_dtype = deprecation.deprecated_argument_lookup(
        "dtype_hint", dtype_hint, "preferred_dtype", preferred_dtype)
    return convert_to_tensor_v2(value, dtype, preferred_dtype, name)
  
  
  @tf_export("convert_to_tensor", v1=[])
  def convert_to_tensor_v2(value, dtype=None, dtype_hint=None, name=None):
    """Converts the given `value` to a `Tensor`.
  
    This function converts Python objects of various types to `Tensor`
    objects. It accepts `Tensor` objects, numpy arrays, Python lists,
    and Python scalars. For example:
  
    >>> def my_func(arg):
    ...   arg = tf.convert_to_tensor(arg, dtype=tf.float32)
    ...   return arg
  
    >>> # The following calls are equivalent.
    >>> value_1 = my_func(tf.constant([[1.0, 2.0], [3.0, 4.0]]))
    >>> print(value_1)
    tf.Tensor(
      [[1. 2.]
       [3. 4.]], shape=(2, 2), dtype=float32)
    >>> value_2 = my_func([[1.0, 2.0], [3.0, 4.0]])
    >>> print(value_2)
    tf.Tensor(
      [[1. 2.]
       [3. 4.]], shape=(2, 2), dtype=float32)
    >>> value_3 = my_func(np.array([[1.0, 2.0], [3.0, 4.0]], dtype=np.float32))
    >>> print(value_3)
    tf.Tensor(
      [[1. 2.]
       [3. 4.]], shape=(2, 2), dtype=float32)
  
    This function can be useful when composing a new operation in Python
    (such as `my_func` in the example above). All standard Python op
    constructors apply this function to each of their Tensor-valued
    inputs, which allows those ops to accept numpy arrays, Python lists,
    and scalars in addition to `Tensor` objects.
  
    Note: This function diverges from default Numpy behavior for `float` and
      `string` types when `None` is present in a Python list or scalar. Rather
      than silently converting `None` values, an error will be thrown.
  
    Args:
      value: An object whose type has a registered `Tensor` conversion function.
      dtype: Optional element type for the returned tensor. If missing, the type
        is inferred from the type of `value`.
      dtype_hint: Optional element type for the returned tensor, used when dtype
        is None. In some cases, a caller may not have a dtype in mind when
        converting to a tensor, so dtype_hint can be used as a soft preference.
        If the conversion to `dtype_hint` is not possible, this argument has no
        effect.
      name: Optional name to use if a new `Tensor` is created.
  
    Returns:
      A `Tensor` based on `value`.
  
    Raises:
      TypeError: If no conversion function is registered for `value` to `dtype`.
      RuntimeError: If a registered conversion function returns an invalid value.
      ValueError: If the `value` is a tensor not of given `dtype` in graph mode.
    """
    return convert_to_tensor(
        value=value,
        dtype=dtype,
        name=name,
        preferred_dtype=dtype_hint,
        as_ref=False)
  
  
  def _error_prefix(name):
    return "" if name is None else "%s: " % name
  
  
  def convert_to_tensor(value,
                        dtype=None,
                        name=None,
                        as_ref=False,
                        preferred_dtype=None,
                        dtype_hint=None,
                        ctx=None,
                        accepted_result_types=(Tensor,)):
    """Implementation of the public convert_to_tensor."""
    # TODO(b/142518781): Fix all call-sites and remove redundant arg
    preferred_dtype = preferred_dtype or dtype_hint
    if isinstance(value, EagerTensor):
      if ctx is None:
        ctx = context.context()
      if not ctx.executing_eagerly():
        graph = get_default_graph()
        if not graph.building_function:
          raise RuntimeError("Attempting to capture an EagerTensor without "
                             "building a function.")
        return graph.capture(value, name=name)
  
    if dtype is not None:
      dtype = dtypes.as_dtype(dtype)
    if isinstance(value, Tensor):
      if dtype is not None and not dtype.is_compatible_with(value.dtype):
        raise ValueError(
            "Tensor conversion requested dtype %s for Tensor with dtype %s: %r" %
            (dtype.name, value.dtype.name, value))
      return value
  
    if preferred_dtype is not None:
      preferred_dtype = dtypes.as_dtype(preferred_dtype)
    for base_type, conversion_func in tensor_conversion_registry.get(type(value)):
      # If dtype is None but preferred_dtype is not None, we try to
      # cast to preferred_dtype first.
      ret = None
      if dtype is None and preferred_dtype is not None:
        try:
          ret = conversion_func(
              value, dtype=preferred_dtype, name=name, as_ref=as_ref)
        except (TypeError, ValueError):
          # Could not coerce the conversion to use the preferred dtype.
          pass
        else:
          if (ret is not NotImplemented and
              ret.dtype.base_dtype != preferred_dtype.base_dtype):
            raise TypeError("convert_to_tensor did not convert to "
                            "the preferred dtype: %s vs %s " %
                            (ret.dtype.base_dtype, preferred_dtype.base_dtype))
  
      if ret is None:
        ret = conversion_func(value, dtype=dtype, name=name, as_ref=as_ref)
  
      if ret is NotImplemented:
        continue
  
      if not isinstance(ret, accepted_result_types):
        raise RuntimeError(
            "%sConversion function %r for type %s returned non-Tensor: %r" %
            (_error_prefix(name), conversion_func, base_type, ret))
      if dtype and not dtype.is_compatible_with(ret.dtype):
        raise RuntimeError(
            "%sConversion function %r for type %s returned incompatible "
            "dtype: requested = %s, actual = %s" %
            (_error_prefix(name), conversion_func, base_type, dtype.name,
             ret.dtype.name))
      return ret
    raise TypeError("%sCannot convert %r with type %s to Tensor: "
                    "no conversion function registered." %
                    (_error_prefix(name), value, type(value)))
  
  
  internal_convert_to_tensor = convert_to_tensor
  
  
  def internal_convert_n_to_tensor(values,
                                   dtype=None,
                                   name=None,
                                   as_ref=False,
                                   preferred_dtype=None,
                                   ctx=None):
    """Converts `values` to a list of `Tensor` objects.
  
    Args:
      values: A list of objects that can be consumed by `tf.convert_to_tensor()`.
      dtype: (Optional.) The required `DType` of the returned `Tensor` objects.
      name: (Optional.) A name prefix to used when a new `Tensor` is created, in
        which case element `i` will be given the name `name + '_' + i`.
      as_ref: True if the caller wants the results as ref tensors.
      preferred_dtype: Optional element type for the returned tensors, used when
        dtype is None. In some cases, a caller may not have a dtype in mind when
        converting to a tensor, so preferred_dtype can be used as a soft
        preference.  If the conversion to `preferred_dtype` is not possible, this
        argument has no effect.
      ctx: The value of context.context().
  
    Returns:
      A list of `Tensor` and/or `IndexedSlices` objects.
  
    Raises:
      TypeError: If no conversion function is registered for an element in
        `values`.
      RuntimeError: If a registered conversion function returns an invalid
        value.
    """
    if not isinstance(values, collections_abc.Sequence):
      raise TypeError("values must be a sequence.")
    ret = []
    if ctx is None:
      ctx = context.context()
    for i, value in enumerate(values):
      n = None if name is None else "%s_%d" % (name, i)
      ret.append(
          convert_to_tensor(
              value,
              dtype=dtype,
              name=n,
              as_ref=as_ref,
              preferred_dtype=preferred_dtype,
              ctx=ctx))
    return ret
  
  
  def convert_n_to_tensor(values, dtype=None, name=None, preferred_dtype=None):
    """Converts `values` to a list of `Tensor` objects.
  
    Args:
      values: A list of objects that can be consumed by `tf.convert_to_tensor()`.
      dtype: (Optional.) The required `DType` of the returned `Tensor` objects.
      name: (Optional.) A name prefix to used when a new `Tensor` is created, in
        which case element `i` will be given the name `name + '_' + i`.
      preferred_dtype: Optional element type for the returned tensors, used when
        dtype is None. In some cases, a caller may not have a dtype in mind when
        converting to a tensor, so preferred_dtype can be used as a soft
        preference.  If the conversion to `preferred_dtype` is not possible, this
        argument has no effect.
  
    Returns:
      A list of `Tensor` and/or `IndexedSlices` objects.
  
    Raises:
      TypeError: If no conversion function is registered for an element in
        `values`.
      RuntimeError: If a registered conversion function returns an invalid
        value.
    """
    return internal_convert_n_to_tensor(
        values=values,
        dtype=dtype,
        name=name,
        preferred_dtype=preferred_dtype,
        as_ref=False)
  
  
  def convert_to_tensor_or_composite(value, dtype=None, name=None):
    """Converts the given object to a `Tensor` or `CompositeTensor`.
  
    If `value` is a `CompositeTensor` it is returned unmodified. Otherwise, it
    is converted to a `Tensor` using `convert_to_tensor()`.
  
    Args:
      value: A `CompositeTensor` or an object that can be consumed by
        `convert_to_tensor()`.
      dtype: (Optional.) The required `DType` of the returned `Tensor` or
        `CompositeTensor`.
      name: (Optional.) A name to use if a new `Tensor` is created.
  
    Returns:
      A `Tensor` or `CompositeTensor`, based on `value`.
  
    Raises:
      ValueError: If `dtype` does not match the element type of `value`.
    """
    return internal_convert_to_tensor_or_composite(
        value=value, dtype=dtype, name=name, as_ref=False)
  
  
  def internal_convert_to_tensor_or_composite(value,
                                              dtype=None,
                                              name=None,
                                              as_ref=False):
    """Converts the given object to a `Tensor` or `CompositeTensor`.
  
    If `value` is a `CompositeTensor` it is returned unmodified.  Otherwise, it
    is converted to a `Tensor` using `convert_to_tensor()`.
  
    Args:
      value: A `CompositeTensor`, or an object that can be consumed by
        `convert_to_tensor()`.
      dtype: (Optional.) The required `DType` of the returned `Tensor` or
        `CompositeTensor`.
      name: (Optional.) A name to use if a new `Tensor` is created.
      as_ref: True if the caller wants the results as ref tensors.
  
    Returns:
      A `Tensor` or `CompositeTensor`, based on `value`.
  
    Raises:
      ValueError: If `dtype` does not match the element type of `value`.
    """
    if isinstance(value, composite_tensor.CompositeTensor):
      value_dtype = getattr(value, "dtype", None)
      if dtype and not dtypes.as_dtype(dtype).is_compatible_with(value_dtype):
        raise ValueError(
            "Tensor conversion requested dtype %s for Tensor with dtype %s: %r" %
            (dtypes.as_dtype(dtype).name, value.dtype.name, str(value)))
      return value
    else:
      return convert_to_tensor(
          value,
          dtype=dtype,
          name=name,
          as_ref=as_ref,
          accepted_result_types=(Tensor, composite_tensor.CompositeTensor))
  
  
  def internal_convert_n_to_tensor_or_composite(values,
                                                dtype=None,
                                                name=None,
                                                as_ref=False):
    """Converts `values` to a list of `Tensor` or `CompositeTensor` objects.
  
    Any `CompositeTensor` objects in `values` are returned unmodified.
  
    Args:
      values: A list of `None`, `CompositeTensor`, or objects that can be consumed
        by `convert_to_tensor()`.
      dtype: (Optional.) The required `DType` of the returned `Tensor`s or
        `CompositeTensor`s.
      name: (Optional.) A name prefix to used when a new `Tensor` is created, in
        which case element `i` will be given the name `name + '_' + i`.
      as_ref: True if the caller wants the results as ref tensors.
  
    Returns:
      A list of `Tensor`, `CompositeTensor`, and/or `None` objects.
  
    Raises:
      TypeError: If no conversion function is registered for an element in
        `values`.
      RuntimeError: If a registered conversion function returns an invalid
        value.
    """
    if not isinstance(values, collections_abc.Sequence):
      raise TypeError("values must be a sequence.")
    ret = []
    for i, value in enumerate(values):
      if value is None:
        ret.append(value)
      else:
        n = None if name is None else "%s_%d" % (name, i)
        ret.append(
            internal_convert_to_tensor_or_composite(
                value, dtype=dtype, name=n, as_ref=as_ref))
    return ret
  
  
  def convert_n_to_tensor_or_composite(values, dtype=None, name=None):
    """Converts `values` to a list of `Output` or `CompositeTensor` objects.
  
    Any `CompositeTensor` objects in `values` are returned unmodified.
  
    Args:
      values: A list of `None`, `CompositeTensor``, or objects that can be
        consumed by `convert_to_tensor()`.
      dtype: (Optional.) The required `DType` of the returned `Tensor`s or
        `CompositeTensor`s.
      name: (Optional.) A name prefix to used when a new `Tensor` is created, in
        which case element `i` will be given the name `name + '_' + i`.
  
    Returns:
      A list of `Tensor` and/or `CompositeTensor` objects.
  
    Raises:
      TypeError: If no conversion function is registered for an element in
        `values`.
      RuntimeError: If a registered conversion function returns an invalid
        value.
    """
    return internal_convert_n_to_tensor_or_composite(
        values=values, dtype=dtype, name=name, as_ref=False)
  
  
  def _device_string(dev_spec):
    if pydev.is_device_spec(dev_spec):
      return dev_spec.to_string()
    else:
      return dev_spec
  
  
  def _NodeDef(op_type, name, attrs=None):
    """Create a NodeDef proto.
  
    Args:
      op_type: Value for the "op" attribute of the NodeDef proto.
      name: Value for the "name" attribute of the NodeDef proto.
      attrs: Dictionary where the key is the attribute name (a string)
        and the value is the respective "attr" attribute of the NodeDef proto (an
        AttrValue).
  
    Returns:
      A node_def_pb2.NodeDef protocol buffer.
    """
    node_def = node_def_pb2.NodeDef(op=compat.as_bytes(op_type),
                                    name=compat.as_bytes(name))
    if attrs:
      for k, v in six.iteritems(attrs):
        node_def.attr[k].CopyFrom(v)
    return node_def
  
  
  # Copied from core/framework/node_def_util.cc
  # TODO(mrry,josh11b): Consolidate this validation in C++ code.
  _VALID_OP_NAME_REGEX = re.compile("^[A-Za-z0-9.][A-Za-z0-9_.\\-/>]*$")
  _VALID_SCOPE_NAME_REGEX = re.compile("^[A-Za-z0-9_.\\-/>]*$")
  
  
  def _create_c_op(graph, node_def, inputs, control_inputs, op_def=None):
    """Creates a TF_Operation.
  
    Args:
      graph: a `Graph`.
      node_def: `node_def_pb2.NodeDef` for the operation to create.
      inputs: A flattened list of `Tensor`s. This function handles grouping
        tensors into lists as per attributes in the `node_def`.
      control_inputs: A list of `Operation`s to set as control dependencies.
      op_def: Optional. `op_def_pb2.OpDef` for the operation to create. If not
        specified, is looked up from the `graph` using `node_def.op`.
  
    Returns:
      A wrapped TF_Operation*.
    """
    if op_def is None:
      op_def = graph._get_op_def(node_def.op)  # pylint: disable=protected-access
    # TODO(skyewm): op_def_library.apply_op() flattens the incoming inputs.
    # Refactor so we don't have to do this here.
    inputs = _reconstruct_sequence_inputs(op_def, inputs, node_def.attr)
    # pylint: disable=protected-access
    op_desc = pywrap_tf_session.TF_NewOperation(graph._c_graph,
                                                compat.as_str(node_def.op),
                                                compat.as_str(node_def.name))
    if node_def.device:
      pywrap_tf_session.TF_SetDevice(op_desc, compat.as_str(node_def.device))
    # Add inputs
    for op_input in inputs:
      if isinstance(op_input, (list, tuple)):
        pywrap_tf_session.TF_AddInputList(op_desc,
                                          [t._as_tf_output() for t in op_input])
      else:
        pywrap_tf_session.TF_AddInput(op_desc, op_input._as_tf_output())
  
    # Add control inputs
    for control_input in control_inputs:
      pywrap_tf_session.TF_AddControlInput(op_desc, control_input._c_op)
    # pylint: enable=protected-access
  
    # Add attrs
    for name, attr_value in node_def.attr.items():
      serialized = attr_value.SerializeToString()
      # TODO(skyewm): this creates and deletes a new TF_Status for every attr.
      # It might be worth creating a convenient way to re-use the same status.
      pywrap_tf_session.TF_SetAttrValueProto(op_desc, compat.as_str(name),
                                             serialized)
  
    try:
      c_op = pywrap_tf_session.TF_FinishOperation(op_desc)
    except errors.InvalidArgumentError as e:
      # Convert to ValueError for backwards compatibility.
      raise ValueError(str(e))
  
    return c_op
  
  
  @tf_export("Operation")
  class Operation(object):
    """Represents a graph node that performs computation on tensors.
  
    An `Operation` is a node in a `tf.Graph` that takes zero or more `Tensor`
    objects as input, and produces zero or more `Tensor` objects as output.
    Objects of type `Operation` are created by calling a Python op constructor
    (such as `tf.matmul`) within a `tf.function` or under a `tf.Graph.as_default`
    context manager.
  
    For example, within a `tf.function`, `c = tf.matmul(a, b)` creates an
    `Operation` of type "MatMul" that takes tensors `a` and `b` as input, and
    produces `c` as output.
  
    If a `tf.compat.v1.Session` is used, an `Operation` of a `tf.Graph` can be
    executed by passing it to `tf.Session.run`. `op.run()` is a shortcut for
    calling `tf.compat.v1.get_default_session().run(op)`.
    """
  
    def __init__(self,
                 node_def,
                 g,
                 inputs=None,
                 output_types=None,
                 control_inputs=None,
                 input_types=None,
                 original_op=None,
                 op_def=None):
      r"""Creates an `Operation`.
  
      NOTE: This constructor validates the name of the `Operation` (passed
      as `node_def.name`). Valid `Operation` names match the following
      regular expression:
  
          [A-Za-z0-9.][A-Za-z0-9_.\\-/]*
  
      Args:
        node_def: `node_def_pb2.NodeDef`.  `NodeDef` for the `Operation`. Used for
          attributes of `node_def_pb2.NodeDef`, typically `name`, `op`, and
          `device`.  The `input` attribute is irrelevant here as it will be
          computed when generating the model.
        g: `Graph`. The parent graph.
        inputs: list of `Tensor` objects. The inputs to this `Operation`.
        output_types: list of `DType` objects.  List of the types of the `Tensors`
          computed by this operation.  The length of this list indicates the
          number of output endpoints of the `Operation`.
        control_inputs: list of operations or tensors from which to have a control
          dependency.
        input_types: List of `DType` objects representing the types of the tensors
          accepted by the `Operation`.  By default uses `[x.dtype.base_dtype for x
          in inputs]`.  Operations that expect reference-typed inputs must specify
          these explicitly.
        original_op: Optional. Used to associate the new `Operation` with an
          existing `Operation` (for example, a replica with the op that was
          replicated).
        op_def: Optional. The `op_def_pb2.OpDef` proto that describes the op type
          that this `Operation` represents.
  
      Raises:
        TypeError: if control inputs are not Operations or Tensors,
          or if `node_def` is not a `NodeDef`,
          or if `g` is not a `Graph`,
          or if `inputs` are not tensors,
          or if `inputs` and `input_types` are incompatible.
        ValueError: if the `node_def` name is not valid.
      """
      # For internal use only: `node_def` can be set to a TF_Operation to create
      # an Operation for that op. This is useful for creating Operations for ops
      # indirectly created by C API methods, e.g. the ops created by
      # TF_ImportGraphDef. When `node_def` is a TF_Operation, all optional fields
      # should be None.
  
      if isinstance(node_def, node_def_pb2.NodeDef):
        if node_def.ByteSize() >= (1 << 31) or node_def.ByteSize() < 0:
          raise ValueError(
              "Cannot create a tensor proto whose content is larger than 2GB.")
        if not _VALID_OP_NAME_REGEX.match(node_def.name):
          raise ValueError("'%s' is not a valid node name" % node_def.name)
        c_op = None
      elif type(node_def).__name__ == "TF_Operation":
        assert inputs is None
        assert output_types is None
        assert control_inputs is None
        assert input_types is None
        assert original_op is None
        assert op_def is None
        c_op = node_def
      else:
        raise TypeError("node_def needs to be a NodeDef: %s" % node_def)
  
      if not isinstance(g, Graph):
        raise TypeError("g needs to be a Graph: %s" % g)
      self._graph = g
  
      if inputs is None:
        inputs = []
      elif not isinstance(inputs, list):
        raise TypeError("inputs needs to be a list of Tensors: %s" % inputs)
      for a in inputs:
        if not isinstance(a, Tensor):
          raise TypeError("input needs to be a Tensor: %s" % a)
      if input_types is None:
        input_types = [i.dtype.base_dtype for i in inputs]
      else:
        if not all(
            x.is_compatible_with(i.dtype) for i, x in zip(inputs, input_types)):
          raise TypeError("In op '%s', input types (%s) are not compatible "
                          "with expected types (%s)" %
                          (node_def.name, [i.dtype for i in inputs], input_types))
  
      # Build the list of control inputs.
      control_input_ops = []
      if control_inputs:
        for c in control_inputs:
          control_op = None
          if isinstance(c, Operation):
            control_op = c
          elif isinstance(c, (Tensor, IndexedSlices)):
            control_op = c.op
          else:
            raise TypeError("Control input must be an Operation, "
                            "a Tensor, or IndexedSlices: %s" % c)
          control_input_ops.append(control_op)
  
      # This will be set by self.inputs.
      self._inputs_val = None
  
      # pylint: disable=protected-access
      self._original_op = original_op
      self._traceback = tf_stack.extract_stack()
  
      # List of _UserDevSpecs holding code location of device context manager
      # invocations and the users original argument to them.
      self._device_code_locations = None
      # Dict mapping op name to file and line information for op colocation
      # context managers.
      self._colocation_code_locations = None
      self._control_flow_context = self.graph._get_control_flow_context()
  
      # Gradient function for this op. There are three ways to specify gradient
      # function, and first available gradient gets used, in the following order.
      # 1. self._gradient_function
      # 2. Gradient name registered by "_gradient_op_type" attribute.
      # 3. Gradient name registered by op.type.
      self._gradient_function = None
  
      # Initialize self._c_op.
      if c_op:
        self._c_op = c_op
        op_def = g._get_op_def(pywrap_tf_session.TF_OperationOpType(c_op))
        name = self.name
      else:
        if op_def is None:
          op_def = self._graph._get_op_def(node_def.op)
        self._c_op = _create_c_op(self._graph, node_def, inputs,
                                  control_input_ops, op_def)
        name = compat.as_str(node_def.name)
      # pylint: enable=protected-access
  
      self._is_stateful = op_def.is_stateful
  
      # Initialize self._outputs.
      num_outputs = pywrap_tf_session.TF_OperationNumOutputs(self._c_op)
      self._outputs = []
      for i in range(num_outputs):
        tf_output = c_api_util.tf_output(self._c_op, i)
        output_type = pywrap_tf_session.TF_OperationOutputType(tf_output)
        tensor = Tensor._create_with_tf_output(self, i, output_type, tf_output)  # pylint: disable=protected-access
        self._outputs.append(tensor)
  
      self._id_value = self._graph._add_op(self, name)  # pylint: disable=protected-access
  
      if not c_op:
        self._control_flow_post_processing(input_tensors=inputs)
  
    def _control_flow_post_processing(self, input_tensors=None):
      """Add this op to its control flow context.
  
      This may add new ops and change this op's inputs. self.inputs must be
      available before calling this method.
  
      Args:
        input_tensors: (Optional.) A list of `Tensors` corresponding to the inputs
          of this op, which should be equivalent to `self.inputs`. Pass this
          argument to avoid evaluating `self.inputs` unnecessarily.
      """
      if input_tensors is None:
        input_tensors = self.inputs
      for input_tensor in input_tensors:
        control_flow_util.CheckInputFromValidContext(self, input_tensor.op)
      if self._control_flow_context is not None:
        self._control_flow_context.AddOp(self)
  
    def colocation_groups(self):
      """Returns the list of colocation groups of the op."""
      default_colocation_group = [compat.as_bytes("loc:@%s" % self.name)]
      try:
        class_attr = self.get_attr("_class")
      except ValueError:
        # This op has no explicit colocation group, so it is itself its
        # own root of a colocation group.
        return default_colocation_group
  
      attr_groups = [
          class_name for class_name in class_attr
          if class_name.startswith(b"loc:@")
      ]
  
      # If there are no colocation groups in the explicit _class field,
      # return the default colocation group.
      return attr_groups if attr_groups else default_colocation_group
  
    def values(self):
      """DEPRECATED: Use outputs."""
      return tuple(self.outputs)
  
    def _get_control_flow_context(self):
      """Returns the control flow context of this op.
  
      Returns:
        A context object.
      """
      return self._control_flow_context
  
    def _set_control_flow_context(self, ctx):
      """Sets the current control flow context of this op.
  
      Args:
        ctx: a context object.
      """
      self._control_flow_context = ctx
  
    @property
    def name(self):
      """The full name of this operation."""
      return pywrap_tf_session.TF_OperationName(self._c_op)
  
    @property
    def _id(self):
      """The unique integer id of this operation."""
      return self._id_value
  
    @property
    def device(self):
      """The name of the device to which this op has been assigned, if any.
  
      Returns:
        The string name of the device to which this op has been
        assigned, or an empty string if it has not been assigned to a
        device.
      """
      return pywrap_tf_session.TF_OperationDevice(self._c_op)
  
    @property
    def _device_assignments(self):
      """Code locations for device context managers active at op creation.
  
      This property will return a list of traceable_stack.TraceableObject
      instances where .obj is a string representing the assigned device
      (or information about the function that would be applied to this op
      to compute the desired device) and the filename and lineno members
      record the location of the relevant device context manager.
  
      For example, suppose file_a contained these lines:
  
        file_a.py:
          15: with tf.device('/gpu:0'):
          16:   node_b = tf.constant(4, name='NODE_B')
  
      Then a TraceableObject t_obj representing the device context manager
      would have these member values:
  
        t_obj.obj -> '/gpu:0'
        t_obj.filename = 'file_a.py'
        t_obj.lineno = 15
  
      and node_b.op._device_assignments would return the list [t_obj].
  
      Returns:
        [str: traceable_stack.TraceableObject, ...] as per this method's
        description, above.
      """
      return self._device_code_locations or []
  
    @property
    def _colocation_dict(self):
      """Code locations for colocation context managers active at op creation.
  
      This property will return a dictionary for which the keys are nodes with
      which this Operation is colocated, and for which the values are
      traceable_stack.TraceableObject instances.  The TraceableObject instances
      record the location of the relevant colocation context manager but have the
      "obj" field set to None to prevent leaking private data.
  
      For example, suppose file_a contained these lines:
  
        file_a.py:
          14: node_a = tf.constant(3, name='NODE_A')
          15: with tf.compat.v1.colocate_with(node_a):
          16:   node_b = tf.constant(4, name='NODE_B')
  
      Then a TraceableObject t_obj representing the colocation context manager
      would have these member values:
  
        t_obj.obj -> None
        t_obj.filename = 'file_a.py'
        t_obj.lineno = 15
  
      and node_b.op._colocation_dict would return the dictionary
  
        { 'NODE_A': t_obj }
  
      Returns:
        {str: traceable_stack.TraceableObject} as per this method's description,
        above.
      """
      locations_dict = self._colocation_code_locations or {}
      return locations_dict.copy()
  
    @property
    def _output_types(self):
      """List this operation's output types.
  
      Returns:
        List of the types of the Tensors computed by this operation.
        Each element in the list is an integer whose value is one of
        the TF_DataType enums defined in pywrap_tf_session.h
        The length of this list indicates the number of output endpoints
        of the operation.
      """
      num_outputs = pywrap_tf_session.TF_OperationNumOutputs(self._c_op)
      output_types = [
          int(pywrap_tf_session.TF_OperationOutputType(self._tf_output(i)))
          for i in xrange(num_outputs)
      ]
  
      return output_types
  
    def _tf_output(self, output_idx):
      """Create and return a new TF_Output for output_idx'th output of this op."""
      tf_output = pywrap_tf_session.TF_Output()
      tf_output.oper = self._c_op
      tf_output.index = output_idx
      return tf_output
  
    def _tf_input(self, input_idx):
      """Create and return a new TF_Input for input_idx'th input of this op."""
      tf_input = pywrap_tf_session.TF_Input()
      tf_input.oper = self._c_op
      tf_input.index = input_idx
      return tf_input
  
    def _set_device(self, device):  # pylint: disable=redefined-outer-name
      """Set the device of this operation.
  
      Args:
        device: string or device..  The device to set.
      """
      self._set_device_from_string(compat.as_str(_device_string(device)))
  
    def _set_device_from_string(self, device_str):
      """Fast path to set device if the type is known to be a string.
  
      This function is called frequently enough during graph construction that
      there are non-trivial performance gains if the caller can guarantee that
      the specified device is already a string.
  
      Args:
        device_str: A string specifying where to place this op.
      """
      pywrap_tf_session.SetRequestedDevice(
          self._graph._c_graph,  # pylint: disable=protected-access
          self._c_op,  # pylint: disable=protected-access
          device_str)
  
    def _update_input(self, index, tensor):
      """Update the input to this operation at the given index.
  
      NOTE: This is for TF internal use only. Please don't use it.
  
      Args:
        index: the index of the input to update.
        tensor: the Tensor to be used as the input at the given index.
  
      Raises:
        TypeError: if tensor is not a Tensor,
          or if input tensor type is not convertible to dtype.
        ValueError: if the Tensor is from a different graph.
      """
      if not isinstance(tensor, Tensor):
        raise TypeError("tensor must be a Tensor: %s" % tensor)
      _assert_same_graph(self, tensor)
  
      # Reset cached inputs.
      self._inputs_val = None
      pywrap_tf_session.UpdateEdge(
          self._graph._c_graph,  # pylint: disable=protected-access
          tensor._as_tf_output(),  # pylint: disable=protected-access
          self._tf_input(index))
  
    def _add_while_inputs(self, tensors):
      """See AddWhileInputHack in python_api.h.
  
      NOTE: This is for TF internal use only. Please don't use it.
  
      Args:
        tensors: list of Tensors
  
      Raises:
        TypeError: if tensor is not a Tensor,
          or if input tensor type is not convertible to dtype.
        ValueError: if the Tensor is from a different graph.
      """
      for tensor in tensors:
        if not isinstance(tensor, Tensor):
          raise TypeError("tensor must be a Tensor: %s" % tensor)
        _assert_same_graph(self, tensor)
  
        # Reset cached inputs.
        self._inputs_val = None
        pywrap_tf_session.AddWhileInputHack(
            self._graph._c_graph,  # pylint: disable=protected-access
            tensor._as_tf_output(),  # pylint: disable=protected-access
            self._c_op)
  
    def _add_control_inputs(self, ops):
      """Add a list of new control inputs to this operation.
  
      Args:
        ops: the list of Operations to add as control input.
  
      Raises:
        TypeError: if ops is not a list of Operations.
        ValueError: if any op in ops is from a different graph.
      """
      for op in ops:
        if not isinstance(op, Operation):
          raise TypeError("op must be an Operation: %s" % op)
        pywrap_tf_session.AddControlInput(
            self._graph._c_graph,  # pylint: disable=protected-access
            self._c_op,  # pylint: disable=protected-access
            op._c_op)  # pylint: disable=protected-access
  
    def _add_control_input(self, op):
      """Add a new control input to this operation.
  
      Args:
        op: the Operation to add as control input.
  
      Raises:
        TypeError: if op is not an Operation.
        ValueError: if op is from a different graph.
      """
      if not isinstance(op, Operation):
        raise TypeError("op must be an Operation: %s" % op)
      pywrap_tf_session.AddControlInput(
          self._graph._c_graph,  # pylint: disable=protected-access
          self._c_op,  # pylint: disable=protected-access
          op._c_op)  # pylint: disable=protected-access
  
    def _remove_all_control_inputs(self):
      """Removes any control inputs to this operation."""
      pywrap_tf_session.RemoveAllControlInputs(self._graph._c_graph, self._c_op)  # pylint: disable=protected-access
  
    def _add_outputs(self, types, shapes):
      """Adds new Tensors to self.outputs.
  
      Note: this is generally unsafe to use. This is used in certain situations in
      conjunction with _set_type_list_attr.
  
      Arguments:
        types: list of DTypes
        shapes: list of TensorShapes
      """
      assert len(types) == len(shapes)
      orig_num_outputs = len(self.outputs)
      for i in range(len(types)):
        t = Tensor(self, orig_num_outputs + i, types[i])
        self._outputs.append(t)
        t.set_shape(shapes[i])
  
    def __str__(self):
      return str(self.node_def)
  
    def __repr__(self):
      return "<tf.Operation '%s' type=%s>" % (self.name, self.type)
  
    @property
    def outputs(self):
      """The list of `Tensor` objects representing the outputs of this op."""
      return self._outputs
  
    @property
    def inputs(self):
      """The sequence of `Tensor` objects representing the data inputs of this op."""
      if self._inputs_val is None:
        # pylint: disable=protected-access
        self._inputs_val = tuple(
            map(self.graph._get_tensor_by_tf_output,
                pywrap_tf_session.GetOperationInputs(self._c_op)))
        # pylint: enable=protected-access
      return self._inputs_val
  
    @property
    def _input_types(self):
      num_inputs = pywrap_tf_session.TF_OperationNumInputs(self._c_op)
      input_types = [
          dtypes.as_dtype(
              pywrap_tf_session.TF_OperationInputType(self._tf_input(i)))
          for i in xrange(num_inputs)
      ]
      return input_types
  
    @property
    def control_inputs(self):
      """The `Operation` objects on which this op has a control dependency.
  
      Before this op is executed, TensorFlow will ensure that the
      operations in `self.control_inputs` have finished executing. This
      mechanism can be used to run ops sequentially for performance
      reasons, or to ensure that the side effects of an op are observed
      in the correct order.
  
      Returns:
        A list of `Operation` objects.
  
      """
      control_c_ops = pywrap_tf_session.TF_OperationGetControlInputs_wrapper(
          self._c_op)
      # pylint: disable=protected-access
      return [
          self.graph._get_operation_by_name_unsafe(
              pywrap_tf_session.TF_OperationName(c_op)) for c_op in control_c_ops
      ]
      # pylint: enable=protected-access
  
    @property
    def _control_outputs(self):
      """The `Operation` objects which have a control dependency on this op.
  
      Before any of the ops in self._control_outputs can execute tensorflow will
      ensure self has finished executing.
  
      Returns:
        A list of `Operation` objects.
  
      """
      control_c_ops = pywrap_tf_session.TF_OperationGetControlOutputs_wrapper(
          self._c_op)
      # pylint: disable=protected-access
      return [
          self.graph._get_operation_by_name_unsafe(
              pywrap_tf_session.TF_OperationName(c_op)) for c_op in control_c_ops
      ]
      # pylint: enable=protected-access
  
    @property
    def type(self):
      """The type of the op (e.g. `"MatMul"`)."""
      return pywrap_tf_session.TF_OperationOpType(self._c_op)
  
    @property
    def graph(self):
      """The `Graph` that contains this operation."""
      return self._graph
  
    @property
    def node_def(self):
      # pylint: disable=line-too-long
      """Returns the `NodeDef` representation of this operation.
  
      Returns:
        A
        [`NodeDef`](https://www.tensorflow.org/code/tensorflow/core/framework/node_def.proto)
        protocol buffer.
      """
      # pylint: enable=line-too-long
      with c_api_util.tf_buffer() as buf:
        pywrap_tf_session.TF_OperationToNodeDef(self._c_op, buf)
        data = pywrap_tf_session.TF_GetBuffer(buf)
      node_def = node_def_pb2.NodeDef()
      node_def.ParseFromString(compat.as_bytes(data))
      return node_def
  
    @property
    def op_def(self):
      # pylint: disable=line-too-long
      """Returns the `OpDef` proto that represents the type of this op.
  
      Returns:
        An
        [`OpDef`](https://www.tensorflow.org/code/tensorflow/core/framework/op_def.proto)
        protocol buffer.
      """
      # pylint: enable=line-too-long
      return self._graph._get_op_def(self.type)
  
    @property
    def traceback(self):
      """Returns the call stack from when this operation was constructed."""
      return self._traceback
  
    def _set_attr(self, attr_name, attr_value):
      """Private method used to set an attribute in the node_def."""
      buf = pywrap_tf_session.TF_NewBufferFromString(
          compat.as_bytes(attr_value.SerializeToString()))
      try:
        self._set_attr_with_buf(attr_name, buf)
      finally:
        pywrap_tf_session.TF_DeleteBuffer(buf)
  
    def _set_attr_with_buf(self, attr_name, attr_buf):
      """Set an attr in the node_def with a pre-allocated buffer."""
      # pylint: disable=protected-access
      pywrap_tf_session.SetAttr(self._graph._c_graph, self._c_op, attr_name,
                                attr_buf)
      # pylint: enable=protected-access
  
    def _set_func_attr(self, attr_name, func_name):
      """Private method used to set a function attribute in the node_def."""
      func = attr_value_pb2.NameAttrList(name=func_name)
      self._set_attr(attr_name, attr_value_pb2.AttrValue(func=func))
  
    def _set_func_list_attr(self, attr_name, func_names):
      """Private method used to set a list(function) attribute in the node_def."""
      funcs = [attr_value_pb2.NameAttrList(name=func_name)
               for func_name in func_names]
      funcs_list = attr_value_pb2.AttrValue.ListValue(func=funcs)
      self._set_attr(attr_name, attr_value_pb2.AttrValue(list=funcs_list))
  
    def _set_type_list_attr(self, attr_name, types):
      """Private method used to set a list(type) attribute in the node_def."""
      if not types:
        return
      if isinstance(types[0], dtypes.DType):
        types = [dt.as_datatype_enum for dt in types]
      types_list = attr_value_pb2.AttrValue.ListValue(type=types)
      self._set_attr(attr_name, attr_value_pb2.AttrValue(list=types_list))
  
    def _set_shape_list_attr(self, attr_name, shapes):
      """Private method used to set a list(shape) attribute in the node_def."""
      shapes = [s.as_proto() for s in shapes]
      shapes_list = attr_value_pb2.AttrValue.ListValue(shape=shapes)
      self._set_attr(attr_name, attr_value_pb2.AttrValue(list=shapes_list))
  
    def _clear_attr(self, attr_name):
      """Private method used to clear an attribute in the node_def."""
      # pylint: disable=protected-access
      pywrap_tf_session.ClearAttr(self._graph._c_graph, self._c_op, attr_name)
      # pylint: enable=protected-access
  
    def get_attr(self, name):
      """Returns the value of the attr of this op with the given `name`.
  
      Args:
        name: The name of the attr to fetch.
  
      Returns:
        The value of the attr, as a Python object.
  
      Raises:
        ValueError: If this op does not have an attr with the given `name`.
      """
      fields = ("s", "i", "f", "b", "type", "shape", "tensor", "func")
      try:
        with c_api_util.tf_buffer() as buf:
          pywrap_tf_session.TF_OperationGetAttrValueProto(self._c_op, name, buf)
          data = pywrap_tf_session.TF_GetBuffer(buf)
      except errors.InvalidArgumentError as e:
        # Convert to ValueError for backwards compatibility.
        raise ValueError(str(e))
      x = attr_value_pb2.AttrValue()
      x.ParseFromString(data)
  
      oneof_value = x.WhichOneof("value")
      if oneof_value is None:
        return []
      if oneof_value == "list":
        for f in fields:
          if getattr(x.list, f):
            if f == "type":
              return [dtypes.as_dtype(t) for t in x.list.type]
            else:
              return list(getattr(x.list, f))
        return []
      if oneof_value == "type":
        return dtypes.as_dtype(x.type)
      assert oneof_value in fields, "Unsupported field type in " + str(x)
      return getattr(x, oneof_value)
  
    def _get_attr_type(self, name):
      """Returns the `DType` value of the attr of this op with the given `name`."""
      try:
        dtype_enum = pywrap_tf_session.TF_OperationGetAttrType(self._c_op, name)
        return _DTYPES_INTERN_TABLE[dtype_enum]
      except errors.InvalidArgumentError as e:
        # Convert to ValueError for backwards compatibility.
        raise ValueError(str(e))
  
    def _get_attr_bool(self, name):
      """Returns the `bool` value of the attr of this op with the given `name`."""
      try:
        return pywrap_tf_session.TF_OperationGetAttrBool(self._c_op, name)
      except errors.InvalidArgumentError as e:
        # Convert to ValueError for backwards compatibility.
        raise ValueError(str(e))
  
    def _get_attr_int(self, name):
      """Returns the `int` value of the attr of this op with the given `name`."""
      try:
        return pywrap_tf_session.TF_OperationGetAttrInt(self._c_op, name)
      except errors.InvalidArgumentError as e:
        # Convert to ValueError for backwards compatibility.
        raise ValueError(str(e))
  
    def run(self, feed_dict=None, session=None):
      """Runs this operation in a `Session`.
  
      Calling this method will execute all preceding operations that
      produce the inputs needed for this operation.
  
      *N.B.* Before invoking `Operation.run()`, its graph must have been
      launched in a session, and either a default session must be
      available, or `session` must be specified explicitly.
  
      Args:
        feed_dict: A dictionary that maps `Tensor` objects to feed values. See
          `tf.Session.run` for a description of the valid feed values.
        session: (Optional.) The `Session` to be used to run to this operation. If
          none, the default session will be used.
      """
      _run_using_default_session(self, feed_dict, self.graph, session)
  
  _gradient_registry = registry.Registry("gradient")
  
  
  @tf_export("RegisterGradient")
  class RegisterGradient(object):
    """A decorator for registering the gradient function for an op type.
  
    This decorator is only used when defining a new op type. For an op
    with `m` inputs and `n` outputs, the gradient function is a function
    that takes the original `Operation` and `n` `Tensor` objects
    (representing the gradients with respect to each output of the op),
    and returns `m` `Tensor` objects (representing the partial gradients
    with respect to each input of the op).
  
    For example, assuming that operations of type `"Sub"` take two
    inputs `x` and `y`, and return a single output `x - y`, the
    following gradient function would be registered:
  
    ```python
    @tf.RegisterGradient("Sub")
    def _sub_grad(unused_op, grad):
      return grad, tf.negative(grad)
    ```
  
    The decorator argument `op_type` is the string type of an
    operation. This corresponds to the `OpDef.name` field for the proto
    that defines the operation.
    """
  
    def __init__(self, op_type):
      """Creates a new decorator with `op_type` as the Operation type.
  
      Args:
        op_type: The string type of an operation. This corresponds to the
          `OpDef.name` field for the proto that defines the operation.
  
      Raises:
        TypeError: If `op_type` is not string.
      """
      if not isinstance(op_type, six.string_types):
        raise TypeError("op_type must be a string")
      self._op_type = op_type
  
    def __call__(self, f):
      """Registers the function `f` as gradient function for `op_type`."""
      _gradient_registry.register(f, self._op_type)
      return f
  
  
  @deprecation.deprecated_endpoints("NotDifferentiable", "NoGradient")
  @tf_export("no_gradient", v1=["no_gradient", "NotDifferentiable", "NoGradient"])
  def no_gradient(op_type):
    """Specifies that ops of type `op_type` is not differentiable.
  
    This function should *not* be used for operations that have a
    well-defined gradient that is not yet implemented.
  
    This function is only used when defining a new op type. It may be
    used for ops such as `tf.size()` that are not differentiable.  For
    example:
  
    ```python
    tf.no_gradient("Size")
    ```
  
    The gradient computed for 'op_type' will then propagate zeros.
  
    For ops that have a well-defined gradient but are not yet implemented,
    no declaration should be made, and an error *must* be thrown if
    an attempt to request its gradient is made.
  
    Args:
      op_type: The string type of an operation. This corresponds to the
        `OpDef.name` field for the proto that defines the operation.
  
    Raises:
      TypeError: If `op_type` is not a string.
  
    """
    if not isinstance(op_type, six.string_types):
      raise TypeError("op_type must be a string")
    _gradient_registry.register(None, op_type)
  
  
  # Aliases for the old names, will be eventually removed.
  NoGradient = no_gradient
  NotDifferentiable = no_gradient
  
  
  def get_gradient_function(op):
    """Returns the function that computes gradients for "op"."""
    if not op.inputs:
      return None
  
    gradient_function = op._gradient_function  # pylint: disable=protected-access
    if gradient_function:
      return gradient_function
  
    try:
      op_type = op.get_attr("_gradient_op_type")
    except ValueError:
      op_type = op.type
    return _gradient_registry.lookup(op_type)
  
  
  def set_shape_and_handle_data_for_outputs(_):
    """No op. TODO(b/74620627): Remove this."""
    pass
  
  
  class OpStats(object):
    """A holder for statistics about an operator.
  
    This class holds information about the resource requirements for an op,
    including the size of its weight parameters on-disk and how many FLOPS it
    requires to execute forward inference.
  
    If you define a new operation, you can create a function that will return a
    set of information about its usage of the CPU and disk space when serialized.
    The function itself takes a Graph object that's been set up so you can call
    methods like get_tensor_by_name to help calculate the results, and a NodeDef
    argument.
  
    """
  
    def __init__(self, statistic_type, value=None):
      """Sets up the initial placeholders for the statistics."""
      self.statistic_type = statistic_type
      self.value = value
  
    @property
    def statistic_type(self):
      return self._statistic_type
  
    @statistic_type.setter
    def statistic_type(self, statistic_type):
      self._statistic_type = statistic_type
  
    @property
    def value(self):
      return self._value
  
    @value.setter
    def value(self, value):
      self._value = value
  
    def __iadd__(self, other):
      if other.statistic_type != self.statistic_type:
        raise ValueError("Can't add an OpStat of type %s to one of %s." %
                         (self.statistic_type, other.statistic_type))
      if self.value is None:
        self.value = other.value
      elif other.value is not None:
        self._value += other.value
      return self
  
  
  _stats_registry = registry.Registry("statistical functions")
  
  
  class RegisterStatistics(object):
    """A decorator for registering the statistics function for an op type.
  
    This decorator can be defined for an op type so that it gives a
    report on the resources used by an instance of an operator, in the
    form of an OpStats object.
  
    Well-known types of statistics include these so far:
  
    - flops: When running a graph, the bulk of the computation happens doing
      numerical calculations like matrix multiplications. This type allows a node
      to return how many floating-point operations it takes to complete. The
      total number of FLOPs for a graph is a good guide to its expected latency.
  
    You can add your own statistics just by picking a new type string, registering
    functions for the ops you care about, and then calling get_stats_for_node_def.
  
    If a statistic for an op is registered multiple times, a KeyError will be
    raised.
  
    Since the statistics is counted on a per-op basis. It is not suitable for
    model parameters (capacity), which is expected to be counted only once, even
    if it is shared by multiple ops. (e.g. RNN)
  
    For example, you can define a new metric called doohickey for a Foo operation
    by placing this in your code:
  
    ```python
    @ops.RegisterStatistics("Foo", "doohickey")
    def _calc_foo_bojangles(unused_graph, unused_node_def):
      return ops.OpStats("doohickey", 20)
    ```
  
    Then in client code you can retrieve the value by making this call:
  
    ```python
    doohickey = ops.get_stats_for_node_def(graph, node_def, "doohickey")
    ```
  
    If the NodeDef is for an op with a registered doohickey function, you'll get
    back the calculated amount in doohickey.value, or None if it's not defined.
  
    """
  
    def __init__(self, op_type, statistic_type):
      """Saves the `op_type` as the `Operation` type."""
      if not isinstance(op_type, six.string_types):
        raise TypeError("op_type must be a string.")
      if "," in op_type:
        raise TypeError("op_type must not contain a comma.")
      self._op_type = op_type
      if not isinstance(statistic_type, six.string_types):
        raise TypeError("statistic_type must be a string.")
      if "," in statistic_type:
        raise TypeError("statistic_type must not contain a comma.")
      self._statistic_type = statistic_type
  
    def __call__(self, f):
      """Registers "f" as the statistics function for "op_type"."""
      _stats_registry.register(f, self._op_type + "," + self._statistic_type)
      return f
  
  
  def get_stats_for_node_def(graph, node, statistic_type):
    """Looks up the node's statistics function in the registry and calls it.
  
    This function takes a Graph object and a NodeDef from a GraphDef, and if
    there's an associated statistics method, calls it and returns a result. If no
    function has been registered for the particular node type, it returns an empty
    statistics object.
  
    Args:
      graph: A Graph object that's been set up with the node's graph.
      node: A NodeDef describing the operator.
      statistic_type: A string identifying the statistic we're interested in.
  
    Returns:
      An OpStats object containing information about resource usage.
    """
  
    try:
      stats_func = _stats_registry.lookup(node.op + "," + statistic_type)
      result = stats_func(graph, node)
    except LookupError:
      result = OpStats(statistic_type)
    return result
  
  
  def name_from_scope_name(name):
    """Returns the name of an op given the name of its scope.
  
    Args:
      name: the name of the scope.
  
    Returns:
      the name of the op (equal to scope name minus any trailing slash).
    """
    return name[:-1] if (name and name[-1] == "/") else name
  
  
  _MUTATION_LOCK_GROUP = 0
  _SESSION_RUN_LOCK_GROUP = 1
  
  
  @tf_export("Graph")
  class Graph(object):
    """A TensorFlow computation, represented as a dataflow graph.
  
    Graphs are used by `tf.function`s to represent the function's computations.
    Each graph contains a set of `tf.Operation` objects, which represent units of
    computation; and `tf.Tensor` objects, which represent the units of data that
    flow between operations.
  
    ### Using graphs directly (deprecated)
  
    A `tf.Graph` can be constructed and used directly without a `tf.function`, as
    was required in TensorFlow 1, but this is deprecated and it is recommended to
    use a `tf.function` instead. If a graph is directly used, other deprecated
    TensorFlow 1 classes are also required to execute the graph, such as a
    `tf.compat.v1.Session`.
  
    A default graph can be registered with the `tf.Graph.as_default` context
    manager. Then, operations will be added to the graph instead of being executed
    eagerly. For example:
  
    ```python
    g = tf.Graph()
    with g.as_default():
      # Define operations and tensors in `g`.
      c = tf.constant(30.0)
      assert c.graph is g
    ```
  
    `tf.compat.v1.get_default_graph()` can be used to obtain the default graph.
  
    Important note: This class *is not* thread-safe for graph construction. All
    operations should be created from a single thread, or external
    synchronization must be provided. Unless otherwise specified, all methods
    are not thread-safe.
  
    A `Graph` instance supports an arbitrary number of "collections"
    that are identified by name. For convenience when building a large
    graph, collections can store groups of related objects: for
    example, the `tf.Variable` uses a collection (named
    `tf.GraphKeys.GLOBAL_VARIABLES`) for
    all variables that are created during the construction of a graph. The caller
    may define additional collections by specifying a new name.
    """
  
    def __init__(self):
      """Creates a new, empty Graph."""
      # Protects core state that can be returned via public accessors.
      # Thread-safety is provided on a best-effort basis to support buggy
      # programs, and is not guaranteed by the public `tf.Graph` API.
      #
      # NOTE(mrry): This does not protect the various stacks. A warning will
      # be reported if these are used from multiple threads
      self._lock = threading.RLock()
      # The group lock synchronizes Session.run calls with methods that create
      # and mutate ops (e.g. Graph.create_op()). This synchronization is
      # necessary because it's illegal to modify an operation after it's been run.
      # The group lock allows any number of threads to mutate ops at the same time
      # but if any modification is going on, all Session.run calls have to wait.
      # Similarly, if one or more Session.run calls are going on, all mutate ops
      # have to wait until all Session.run calls have finished.
      self._group_lock = lock_util.GroupLock(num_groups=2)
      self._nodes_by_id = {}  # GUARDED_BY(self._lock)
      self._next_id_counter = 0  # GUARDED_BY(self._lock)
      self._nodes_by_name = {}  # GUARDED_BY(self._lock)
      self._version = 0  # GUARDED_BY(self._lock)
      # Maps a name used in the graph to the next id to use for that name.
      self._names_in_use = {}
      self._stack_state_is_thread_local = False
      self._thread_local = threading.local()
      # Functions that will be applied to choose a device if none is specified.
      # In TF2.x or after switch_to_thread_local(),
      # self._thread_local._device_function_stack is used instead.
      self._graph_device_function_stack = traceable_stack.TraceableStack()
      # Default original_op applied to new ops.
      self._default_original_op = None
      # Current control flow context. It could be either CondContext or
      # WhileContext defined in ops/control_flow_ops.py
      self._control_flow_context = None
      # A new node will depend of the union of all of the nodes in the stack.
      # In TF2.x or after switch_to_thread_local(),
      # self._thread_local._control_dependencies_stack is used instead.
      self._graph_control_dependencies_stack = []
      # Arbitrary collections of objects.
      self._collections = {}
      # The graph-level random seed
      self._seed = None
      # A dictionary of attributes that should be applied to all ops.
      self._attr_scope_map = {}
      # A map from op type to the kernel label that should be used.
      self._op_to_kernel_label_map = {}
      # A map from op type to an alternative op type that should be used when
      # computing gradients.
      self._gradient_override_map = {}
      # A map from op type to a gradient function that should be used instead.
      self._gradient_function_map = {}
      # True if the graph is considered "finalized".  In that case no
      # new operations can be added.
      self._finalized = False
      # Functions defined in the graph
      self._functions = collections.OrderedDict()
      # Default GraphDef versions
      self._graph_def_versions = versions_pb2.VersionDef(
          producer=versions.GRAPH_DEF_VERSION,
          min_consumer=versions.GRAPH_DEF_VERSION_MIN_CONSUMER)
      self._building_function = False
      # Stack of colocate_with ops. In TF2.x or after switch_to_thread_local(),
      # self._thread_local._colocation_stack is used instead.
      self._graph_colocation_stack = traceable_stack.TraceableStack()
      # Set of tensors that are dangerous to feed!
      self._unfeedable_tensors = object_identity.ObjectIdentitySet()
      # Set of operations that are dangerous to fetch!
      self._unfetchable_ops = set()
      # A map of tensor handle placeholder to tensor dtype.
      self._handle_feeders = {}
      # A map from tensor handle to its read op.
      self._handle_readers = {}
      # A map from tensor handle to its move op.
      self._handle_movers = {}
      # A map from tensor handle to its delete op.
      self._handle_deleters = {}
      # Allow optimizers and other objects to pseudo-uniquely key graphs (this key
      # will be shared when defining function graphs, for example, so optimizers
      # being called inside function definitions behave as if they were seeing the
      # actual outside graph).
      self._graph_key = "grap-key-%d/" % (uid(),)
      # A string with the last reduction method passed to
      # losses.compute_weighted_loss(), or None. This is required only for
      # backward compatibility with Estimator and optimizer V1 use cases.
      self._last_loss_reduction = None
      # Flag that is used to indicate whether loss has been scaled by optimizer.
      # If this flag has been set, then estimator uses it to scale losss back
      # before reporting. This is required only for backward compatibility with
      # Estimator and optimizer V1 use cases.
      self._is_loss_scaled_by_optimizer = False
      self._container = ""
      # Set to True if this graph is being built in an
      # AutomaticControlDependencies context.
      self._add_control_dependencies = False
      # Cache for OpDef protobufs retrieved via the C API.
      self._op_def_cache = {}
      # Cache for constant results of `broadcast_gradient_args()`. The keys are
      # tuples of fully-defined shapes: (x_shape_tuple, y_shape_tuple), and the
      # values are tuples of reduction indices: (rx, ry).
      self._bcast_grad_args_cache = {}
      # Cache for constant results of `reduced_shape()`. The keys are pairs of
      # tuples: (input_shape_tuple, reduction_indices_tuple), and the values
      # are pairs of tuples: (output_shape_kept_dims, tile_scaling).
      self._reduced_shape_cache = {}
  
      # TODO(skyewm): fold as much of the above as possible into the C
      # implementation
      self._scoped_c_graph = c_api_util.ScopedTFGraph()
      # The C API requires all ops to have shape functions. Disable this
      # requirement (many custom ops do not have shape functions, and we don't
      # want to break these existing cases).
      pywrap_tf_session.SetRequireShapeInferenceFns(self._c_graph, False)
      if tf2.enabled():
        self.switch_to_thread_local()
  
    # Note: this method is private because the API of tf.Graph() is public and
    # frozen, and this functionality is still not ready for public visibility.
    @tf_contextlib.contextmanager
    def _variable_creator_scope(self, creator, priority=100):
      """Scope which defines a variable creation function.
  
      Args:
        creator: A callable taking `next_creator` and `kwargs`. See the
          `tf.variable_creator_scope` docstring.
        priority: Creators with a higher `priority` are called first. Within the
          same priority, creators are called inner-to-outer.
  
      Yields:
        `_variable_creator_scope` is a context manager with a side effect, but
        doesn't return a value.
  
      Raises:
        RuntimeError: If variable creator scopes are not properly nested.
      """
      # This step keeps a reference to the existing stack, and it also initializes
      # self._thread_local._variable_creator_stack if it doesn't exist yet.
      old = self._variable_creator_stack
      new = list(old)
      new.append((priority, creator))
      # Sorting is stable, so we'll put higher-priority creators later in the list
      # but otherwise maintain registration order.
      new.sort(key=lambda item: item[0])
      self._thread_local._variable_creator_stack = new  # pylint: disable=protected-access
      try:
        yield
      finally:
        if self._thread_local._variable_creator_stack is not new:  # pylint: disable=protected-access
          raise RuntimeError(
              "Exiting variable_creator_scope without proper nesting.")
        self._thread_local._variable_creator_stack = old  # pylint: disable=protected-access
  
    # Note: this method is private because the API of tf.Graph() is public and
    # frozen, and this functionality is still not ready for public visibility.
    @property
    def _variable_creator_stack(self):
      if not hasattr(self._thread_local, "_variable_creator_stack"):
        self._thread_local._variable_creator_stack = []  # pylint: disable=protected-access
  
      # This previously returned a copy of the stack instead of the stack itself,
      # to guard against accidental mutation. Consider, however, code that wants
      # to save and restore the variable creator stack:
      #     def f():
      #       original_stack = graph._variable_creator_stack
      #       graph._variable_creator_stack = new_stack
      #       ...  # Some code
      #       graph._variable_creator_stack = original_stack
      #
      # And lets say you have some code that calls this function with some
      # variable_creator:
      #     def g():
      #       with variable_scope.variable_creator_scope(creator):
      #         f()
      # When exiting the variable creator scope, it would see a different stack
      # object than it expected leading to a "Exiting variable_creator_scope
      # without proper nesting" error.
      return self._thread_local._variable_creator_stack  # pylint: disable=protected-access
  
    @_variable_creator_stack.setter
    def _variable_creator_stack(self, variable_creator_stack):
      self._thread_local._variable_creator_stack = variable_creator_stack  # pylint: disable=protected-access
  
    def _check_not_finalized(self):
      """Check if the graph is finalized.
  
      Raises:
        RuntimeError: If the graph finalized.
      """
      if self._finalized:
        raise RuntimeError("Graph is finalized and cannot be modified.")
  
    def _add_op(self, op, op_name):
      """Adds 'op' to the graph and returns the unique ID for the added Operation.
  
      Args:
        op: the Operation to add.
        op_name: the name of the Operation.
  
      Returns:
        An integer that is a unique ID for the added Operation.
      """
      self._check_not_finalized()
      with self._lock:
        self._next_id_counter += 1
        op_id = self._next_id_counter
        self._nodes_by_id[op_id] = op
        self._nodes_by_name[op_name] = op
        self._version = max(self._version, op_id)
        return op_id
  
    @property
    def _c_graph(self):
      if self._scoped_c_graph:
        return self._scoped_c_graph.graph
      return None
  
    @property
    def version(self):
      """Returns a version number that increases as ops are added to the graph.
  
      Note that this is unrelated to the
      `tf.Graph.graph_def_versions`.
  
      Returns:
         An integer version that increases as ops are added to the graph.
      """
      if self._finalized:
        return self._version
  
      with self._lock:
        return self._version
  
    @property
    def graph_def_versions(self):
      # pylint: disable=line-too-long
      """The GraphDef version information of this graph.
  
      For details on the meaning of each version, see
      [`GraphDef`](https://www.tensorflow.org/code/tensorflow/core/framework/graph.proto).
  
      Returns:
        A `VersionDef`.
      """
      # pylint: enable=line-too-long
      with c_api_util.tf_buffer() as buf:
        pywrap_tf_session.TF_GraphVersions(self._c_graph, buf)
        data = pywrap_tf_session.TF_GetBuffer(buf)
      version_def = versions_pb2.VersionDef()
      version_def.ParseFromString(compat.as_bytes(data))
      return version_def
  
    @property
    def seed(self):
      """The graph-level random seed of this graph."""
      return self._seed
  
    @seed.setter
    def seed(self, seed):
      self._seed = seed
  
    @property
    def finalized(self):
      """True if this graph has been finalized."""
      return self._finalized
  
    def finalize(self):
      """Finalizes this graph, making it read-only.
  
      After calling `g.finalize()`, no new operations can be added to
      `g`.  This method is used to ensure that no operations are added
      to a graph when it is shared between multiple threads, for example
      when using a `tf.compat.v1.train.QueueRunner`.
      """
      self._finalized = True
  
    def _unsafe_unfinalize(self):
      """Opposite of `finalize`.
  
      Internal interface.
  
      NOTE: Unfinalizing a graph could have negative impact on performance,
      especially in a multi-threaded environment.  Unfinalizing a graph
      when it is in use by a Session may lead to undefined behavior. Ensure
      that all sessions using a graph are closed before calling this method.
      """
      self._finalized = False
  
    def _get_control_flow_context(self):
      """Returns the current control flow context.
  
      Returns:
        A context object.
      """
      return self._control_flow_context
  
    def _set_control_flow_context(self, ctx):
      """Sets the current control flow context.
  
      Args:
        ctx: a context object.
      """
      self._control_flow_context = ctx
  
    def _copy_functions_to_graph_def(self, graph_def, starting_bytesize):
      """If this graph contains functions, copy them to `graph_def`."""
      bytesize = starting_bytesize
      for f in self._functions.values():
        bytesize += f.definition.ByteSize()
        if bytesize >= (1 << 31) or bytesize < 0:
          raise ValueError("GraphDef cannot be larger than 2GB.")
        graph_def.library.function.extend([f.definition])
        if f.grad_func_name:
          grad_def = function_pb2.GradientDef()
          grad_def.function_name = f.name
          grad_def.gradient_func = f.grad_func_name
          graph_def.library.gradient.extend([grad_def])
  
    def _as_graph_def(self, from_version=None, add_shapes=False):
      # pylint: disable=line-too-long
      """Returns a serialized `GraphDef` representation of this graph.
  
      The serialized `GraphDef` can be imported into another `Graph`
      (using `tf.import_graph_def`) or used with the
      [C++ Session API](../../../../api_docs/cc/index.md).
  
      This method is thread-safe.
  
      Args:
        from_version: Optional.  If this is set, returns a `GraphDef` containing
          only the nodes that were added to this graph since its `version`
          property had the given value.
        add_shapes: If true, adds an "_output_shapes" list attr to each node with
          the inferred shapes of each of its outputs.
  
      Returns:
        A tuple containing a
        [`GraphDef`](https://www.tensorflow.org/code/tensorflow/core/framework/graph.proto)
        protocol buffer, and the version of the graph to which that
        `GraphDef` corresponds.
  
      Raises:
        ValueError: If the `graph_def` would be too large.
  
      """
      # pylint: enable=line-too-long
      with self._lock:
        with c_api_util.tf_buffer() as buf:
          pywrap_tf_session.TF_GraphToGraphDef(self._c_graph, buf)
          data = pywrap_tf_session.TF_GetBuffer(buf)
        graph = graph_pb2.GraphDef()
        graph.ParseFromString(compat.as_bytes(data))
        # Strip the experimental library field iff it's empty.
        if not graph.library.function:
          graph.ClearField("library")
  
        if add_shapes:
          for node in graph.node:
            op = self._nodes_by_name[node.name]
            if op.outputs:
              node.attr["_output_shapes"].list.shape.extend(
                  [output.get_shape().as_proto() for output in op.outputs])
          for function_def in graph.library.function:
            defined_function = self._functions[function_def.signature.name]
            try:
              func_graph = defined_function.graph
            except AttributeError:
              # _DefinedFunction doesn't have a graph, _EagerDefinedFunction
              # does. Both rely on ops.py, so we can't really isinstance check
              # them.
              continue
            input_shapes = function_def.attr["_input_shapes"]
            try:
              func_graph_inputs = func_graph.inputs
            except AttributeError:
              continue
            # TODO(b/141471245): Fix the inconsistency when inputs of func graph
            # are appended during gradient computation of while/cond.
            for input_tensor, _ in zip(func_graph_inputs,
                                       function_def.signature.input_arg):
              if input_tensor.dtype == dtypes.resource:
                # TODO(allenl): Save and restore handle data, then save the
                # resource placeholder's shape. Right now some shape functions get
                # confused if we set the shape of the resource placeholder (to a
                # scalar of course) and there isn't any handle data.
                input_shapes.list.shape.add().CopyFrom(
                    tensor_shape.TensorShape(None).as_proto())
              else:
                input_shapes.list.shape.add().CopyFrom(
                    input_tensor.get_shape().as_proto())
            for node in function_def.node_def:
              try:
                op = func_graph.get_operation_by_name(node.name)
              except KeyError:
                continue
              outputs = op.outputs
  
              if op.type == "StatefulPartitionedCall":
                # Filter out any extra outputs (possibly added by function
                # backpropagation rewriting).
                num_outputs = len(node.attr["Tout"].list.type)
                outputs = outputs[:num_outputs]
  
              node.attr["_output_shapes"].list.shape.extend(
                  [output.get_shape().as_proto() for output in outputs])
  
      return graph, self._version
  
    def as_graph_def(self, from_version=None, add_shapes=False):
      # pylint: disable=line-too-long
      """Returns a serialized `GraphDef` representation of this graph.
  
      The serialized `GraphDef` can be imported into another `Graph`
      (using `tf.import_graph_def`) or used with the
      [C++ Session API](../../api_docs/cc/index.md).
  
      This method is thread-safe.
  
      Args:
        from_version: Optional.  If this is set, returns a `GraphDef` containing
          only the nodes that were added to this graph since its `version`
          property had the given value.
        add_shapes: If true, adds an "_output_shapes" list attr to each node with
          the inferred shapes of each of its outputs.
  
      Returns:
        A
        [`GraphDef`](https://www.tensorflow.org/code/tensorflow/core/framework/graph.proto)
        protocol buffer.
  
      Raises:
        ValueError: If the `graph_def` would be too large.
      """
      # pylint: enable=line-too-long
      result, _ = self._as_graph_def(from_version, add_shapes)
      return result
  
    def _is_function(self, name):
      """Tests whether 'name' is registered in this graph's function library.
  
      Args:
        name: string op name.
  
      Returns:
        bool indicating whether or not 'name' is registered in function library.
      """
      return compat.as_str(name) in self._functions
  
    def _get_function(self, name):
      """Returns the function definition for 'name'.
  
      Args:
        name: string function name.
  
      Returns:
        The function def proto.
      """
      return self._functions.get(compat.as_str(name), None)
  
    def _add_function(self, function):
      """Adds a function to the graph.
  
      After the function has been added, you can call to the function by
      passing the function name in place of an op name to
      `Graph.create_op()`.
  
      Args:
        function: A `_DefinedFunction` object.
  
      Raises:
        ValueError: if another function is defined with the same name.
      """
      name = function.name
      # Sanity checks on gradient definition.
      if (function.grad_func_name is not None) and (function.python_grad_func is
                                                    not None):
        raise ValueError("Gradient defined twice for function %s" % name)
  
      # Add function to graph
      # pylint: disable=protected-access
      gradient = (
          function._grad_func._c_func.func if function._grad_func else None)
      pywrap_tf_session.TF_GraphCopyFunction(self._c_graph, function._c_func.func,
                                             gradient)
      # pylint: enable=protected-access
  
      self._functions[compat.as_str(name)] = function
  
      # Need a new-enough consumer to support the functions we add to the graph.
      if self._graph_def_versions.min_consumer < 12:
        self._graph_def_versions.min_consumer = 12
  
    @property
    def building_function(self):
      """Returns True iff this graph represents a function."""
      return self._building_function
  
    # Helper functions to create operations.
    @deprecated_args(None,
                     "Shapes are always computed; don't use the compute_shapes "
                     "as it has no effect.", "compute_shapes")
    def create_op(
        self,
        op_type,
        inputs,
        dtypes=None,  # pylint: disable=redefined-outer-name
        input_types=None,
        name=None,
        attrs=None,
        op_def=None,
        compute_shapes=True,
        compute_device=True):
      """Creates an `Operation` in this graph.
  
      This is a low-level interface for creating an `Operation`. Most
      programs will not call this method directly, and instead use the
      Python op constructors, such as `tf.constant()`, which add ops to
      the default graph.
  
      Args:
        op_type: The `Operation` type to create. This corresponds to the
          `OpDef.name` field for the proto that defines the operation.
        inputs: A list of `Tensor` objects that will be inputs to the `Operation`.
        dtypes: (Optional) A list of `DType` objects that will be the types of the
          tensors that the operation produces.
        input_types: (Optional.) A list of `DType`s that will be the types of the
          tensors that the operation consumes. By default, uses the base `DType`
          of each input in `inputs`. Operations that expect reference-typed inputs
          must specify `input_types` explicitly.
        name: (Optional.) A string name for the operation. If not specified, a
          name is generated based on `op_type`.
        attrs: (Optional.) A dictionary where the key is the attribute name (a
          string) and the value is the respective `attr` attribute of the
          `NodeDef` proto that will represent the operation (an `AttrValue`
          proto).
        op_def: (Optional.) The `OpDef` proto that describes the `op_type` that
          the operation will have.
        compute_shapes: (Optional.) Deprecated. Has no effect (shapes are always
          computed).
        compute_device: (Optional.) If True, device functions will be executed to
          compute the device property of the Operation.
  
      Raises:
        TypeError: if any of the inputs is not a `Tensor`.
        ValueError: if colocation conflicts with existing device assignment.
  
      Returns:
        An `Operation` object.
      """
      del compute_shapes
      for idx, a in enumerate(inputs):
        if not isinstance(a, Tensor):
          raise TypeError("Input #%d is not a tensor: %s" % (idx, a))
      return self._create_op_internal(op_type, inputs, dtypes, input_types, name,
                                      attrs, op_def, compute_device)
  
    def _create_op_internal(
        self,
        op_type,
        inputs,
        dtypes=None,  # pylint: disable=redefined-outer-name
        input_types=None,
        name=None,
        attrs=None,
        op_def=None,
        compute_device=True):
      """Creates an `Operation` in this graph.
  
      Implements `Graph.create_op()` without the overhead of the deprecation
      wrapper.
  
      Args:
        op_type: The `Operation` type to create. This corresponds to the
          `OpDef.name` field for the proto that defines the operation.
        inputs: A list of `Tensor` objects that will be inputs to the `Operation`.
        dtypes: (Optional) A list of `DType` objects that will be the types of the
          tensors that the operation produces.
        input_types: (Optional.) A list of `DType`s that will be the types of the
          tensors that the operation consumes. By default, uses the base `DType`
          of each input in `inputs`. Operations that expect reference-typed inputs
          must specify `input_types` explicitly.
        name: (Optional.) A string name for the operation. If not specified, a
          name is generated based on `op_type`.
        attrs: (Optional.) A dictionary where the key is the attribute name (a
          string) and the value is the respective `attr` attribute of the
          `NodeDef` proto that will represent the operation (an `AttrValue`
          proto).
        op_def: (Optional.) The `OpDef` proto that describes the `op_type` that
          the operation will have.
        compute_device: (Optional.) If True, device functions will be executed to
          compute the device property of the Operation.
  
      Raises:
        ValueError: if colocation conflicts with existing device assignment.
  
      Returns:
        An `Operation` object.
      """
      self._check_not_finalized()
      if name is None:
        name = op_type
      # If a names ends with a '/' it is a "name scope" and we use it as-is,
      # after removing the trailing '/'.
      if name and name[-1] == "/":
        name = name_from_scope_name(name)
      else:
        name = self.unique_name(name)
  
      node_def = _NodeDef(op_type, name, attrs)
  
      input_ops = set(t.op for t in inputs)
      control_inputs = self._control_dependencies_for_inputs(input_ops)
      # _create_op_helper mutates the new Operation. `_mutation_lock` ensures a
      # Session.run call cannot occur between creating and mutating the op.
      with self._mutation_lock():
        ret = Operation(
            node_def,
            self,
            inputs=inputs,
            output_types=dtypes,
            control_inputs=control_inputs,
            input_types=input_types,
            original_op=self._default_original_op,
            op_def=op_def)
        self._create_op_helper(ret, compute_device=compute_device)
      return ret
  
    def _create_op_from_tf_operation(self, c_op, compute_device=True):
      """Creates an `Operation` in this graph from the supplied TF_Operation.
  
      This method is like create_op() except the new Operation is constructed
      using `c_op`. The returned Operation will have `c_op` as its _c_op
      field. This is used to create Operation objects around TF_Operations created
      indirectly by the C API (e.g. by TF_ImportGraphDef, TF_FinishWhile).
  
      This function does not call Operation._control_flow_post_processing or
      Graph._control_dependencies_for_inputs (since the inputs may not be
      available yet). The caller is responsible for calling these methods.
  
      Args:
        c_op: a wrapped TF_Operation
        compute_device: (Optional.) If True, device functions will be executed to
          compute the device property of the Operation.
  
      Returns:
        An `Operation` object.
      """
      self._check_not_finalized()
      ret = Operation(c_op, self)
      # If a name_scope was created with ret.name but no nodes were created in it,
      # the name will still appear in _names_in_use even though the name hasn't
      # been used. This is ok, just leave _names_in_use as-is in this case.
      # TODO(skyewm): make the C API guarantee no name conflicts.
      name_key = ret.name.lower()
      if name_key not in self._names_in_use:
        self._names_in_use[name_key] = 1
      self._create_op_helper(ret, compute_device=compute_device)
      return ret
  
    def _create_op_helper(self, op, compute_device=True):
      """Common logic for creating an op in this graph."""
      # Apply any additional attributes requested. Do not overwrite any existing
      # attributes.
      for key, value in self._attr_scope_map.items():
        try:
          op.get_attr(key)
        except ValueError:
          if callable(value):
            value = value(op.node_def)
            if not isinstance(value, (type(None), attr_value_pb2.AttrValue)):
              raise TypeError(
                  "Callable for scope map key '%s' must return either None or "
                  "an AttrValue protocol buffer; but it returned: %s" %
                  (key, value))
          if value:
            op._set_attr(key, value)  # pylint: disable=protected-access
  
      # Apply a kernel label if one has been specified for this op type.
      try:
        kernel_label = self._op_to_kernel_label_map[op.type]
        op._set_attr("_kernel",  # pylint: disable=protected-access
                     attr_value_pb2.AttrValue(s=compat.as_bytes(kernel_label)))
      except KeyError:
        pass
  
      op._gradient_function = self._gradient_function_map.get(op.type)  # pylint: disable=protected-access
  
      # Apply the overriding op type for gradients if one has been specified for
      # this op type.
      try:
        mapped_op_type = self._gradient_override_map[op.type]
        op._set_attr("_gradient_op_type",  # pylint: disable=protected-access
                     attr_value_pb2.AttrValue(s=compat.as_bytes(mapped_op_type)))
      except KeyError:
        pass
  
      self._record_op_seen_by_control_dependencies(op)
  
      if compute_device:
        self._apply_device_functions(op)
  
      # Snapshot the colocation stack metadata before we might generate error
      # messages using it.  Note that this snapshot depends on the actual stack
      # and is independent of the op's _class attribute.
      # pylint: disable=protected-access
      op._colocation_code_locations = self._snapshot_colocation_stack_metadata()
      # pylint: enable=protected-access
  
      if self._colocation_stack:
        all_colocation_groups = []
        for colocation_op in self._colocation_stack.peek_objs():
          all_colocation_groups.extend(colocation_op.colocation_groups())
          if colocation_op.device:
            # pylint: disable=protected-access
            op._set_device(colocation_op.device)
            # pylint: enable=protected-access
  
        all_colocation_groups = sorted(set(all_colocation_groups))
        # pylint: disable=protected-access
        op._set_attr(
            "_class",
            attr_value_pb2.AttrValue(
                list=attr_value_pb2.AttrValue.ListValue(s=all_colocation_groups)))
        # pylint: enable=protected-access
  
      # Sets "container" attribute if
      # (1) self._container is not None
      # (2) "is_stateful" is set in OpDef
      # (3) "container" attribute is in OpDef
      # (4) "container" attribute is None
      if self._container and op._is_stateful:  # pylint: disable=protected-access
        try:
          container_attr = op.get_attr("container")
        except ValueError:
          # "container" attribute is not in OpDef
          pass
        else:
          if not container_attr:
            op._set_attr("container", attr_value_pb2.AttrValue(  # pylint: disable=protected-access
                s=compat.as_bytes(self._container)))
  
    def _add_new_tf_operations(self, compute_devices=True):
      """Creates `Operations` in this graph for any new TF_Operations.
  
      This is useful for when TF_Operations are indirectly created by the C API
      outside of the Operation constructor (e.g. by TF_ImportGraphDef,
      TF_FinishWhile). This ensures there are corresponding Operations for all
      TF_Operations in the underlying TF_Graph.
  
      Args:
        compute_devices: (Optional.) If True, device functions will be executed to
          compute the device properties of each new Operation.
  
      Returns:
        A list of the new `Operation` objects.
      """
      # Create all Operation objects before accessing their inputs since an op may
      # be created before its inputs.
      new_ops = [
          self._create_op_from_tf_operation(c_op, compute_device=compute_devices)
          for c_op in c_api_util.new_tf_operations(self)
      ]
  
      # pylint: disable=protected-access
      for op in new_ops:
        new_control_inputs = self._control_dependencies_for_inputs(op.inputs)
        op._add_control_inputs(new_control_inputs)
        op._control_flow_post_processing()
      # pylint: enable=protected-access
  
      return new_ops
  
    def as_graph_element(self, obj, allow_tensor=True, allow_operation=True):
      """Returns the object referred to by `obj`, as an `Operation` or `Tensor`.
  
      This function validates that `obj` represents an element of this
      graph, and gives an informative error message if it is not.
  
      This function is the canonical way to get/validate an object of
      one of the allowed types from an external argument reference in the
      Session API.
  
      This method may be called concurrently from multiple threads.
  
      Args:
        obj: A `Tensor`, an `Operation`, or the name of a tensor or operation. Can
          also be any object with an `_as_graph_element()` method that returns a
          value of one of these types. Note: `_as_graph_element` will be called
          inside the graph's lock and so may not modify the graph.
        allow_tensor: If true, `obj` may refer to a `Tensor`.
        allow_operation: If true, `obj` may refer to an `Operation`.
  
      Returns:
        The `Tensor` or `Operation` in the Graph corresponding to `obj`.
  
      Raises:
        TypeError: If `obj` is not a type we support attempting to convert
          to types.
        ValueError: If `obj` is of an appropriate type but invalid. For
          example, an invalid string.
        KeyError: If `obj` is not an object in the graph.
      """
      if self._finalized:
        return self._as_graph_element_locked(obj, allow_tensor, allow_operation)
  
      with self._lock:
        return self._as_graph_element_locked(obj, allow_tensor, allow_operation)
  
    def _as_graph_element_locked(self, obj, allow_tensor, allow_operation):
      """See `Graph.as_graph_element()` for details."""
      # The vast majority of this function is figuring
      # out what an API user might be doing wrong, so
      # that we can give helpful error messages.
      #
      # Ideally, it would be nice to split it up, but we
      # need context to generate nice error messages.
  
      if allow_tensor and allow_operation:
        types_str = "Tensor or Operation"
      elif allow_tensor:
        types_str = "Tensor"
      elif allow_operation:
        types_str = "Operation"
      else:
        raise ValueError("allow_tensor and allow_operation can't both be False.")
  
      temp_obj = _as_graph_element(obj)
      if temp_obj is not None:
        obj = temp_obj
  
      # If obj appears to be a name...
      if isinstance(obj, compat.bytes_or_text_types):
        name = compat.as_str(obj)
  
        if ":" in name and allow_tensor:
          # Looks like a Tensor name and can be a Tensor.
          try:
            op_name, out_n = name.split(":")
            out_n = int(out_n)
          except:
            raise ValueError("The name %s looks a like a Tensor name, but is "
                             "not a valid one. Tensor names must be of the "
                             "form \"<op_name>:<output_index>\"." % repr(name))
          if op_name in self._nodes_by_name:
            op = self._nodes_by_name[op_name]
          else:
            raise KeyError("The name %s refers to a Tensor which does not "
                           "exist. The operation, %s, does not exist in the "
                           "graph." % (repr(name), repr(op_name)))
          try:
            return op.outputs[out_n]
          except:
            raise KeyError("The name %s refers to a Tensor which does not "
                           "exist. The operation, %s, exists but only has "
                           "%s outputs." %
                           (repr(name), repr(op_name), len(op.outputs)))
  
        elif ":" in name and not allow_tensor:
          # Looks like a Tensor name but can't be a Tensor.
          raise ValueError("Name %s appears to refer to a Tensor, not a %s." %
                           (repr(name), types_str))
  
        elif ":" not in name and allow_operation:
          # Looks like an Operation name and can be an Operation.
          if name not in self._nodes_by_name:
            raise KeyError("The name %s refers to an Operation not in the "
                           "graph." % repr(name))
          return self._nodes_by_name[name]
  
        elif ":" not in name and not allow_operation:
          # Looks like an Operation name but can't be an Operation.
          if name in self._nodes_by_name:
            # Yep, it's an Operation name
            err_msg = ("The name %s refers to an Operation, not a %s." %
                       (repr(name), types_str))
          else:
            err_msg = ("The name %s looks like an (invalid) Operation name, "
                       "not a %s." % (repr(name), types_str))
          err_msg += (" Tensor names must be of the form "
                      "\"<op_name>:<output_index>\".")
          raise ValueError(err_msg)
  
      elif isinstance(obj, Tensor) and allow_tensor:
        # Actually obj is just the object it's referring to.
        if obj.graph is not self:
          raise ValueError("Tensor %s is not an element of this graph." % obj)
        return obj
      elif isinstance(obj, Operation) and allow_operation:
        # Actually obj is just the object it's referring to.
        if obj.graph is not self:
          raise ValueError("Operation %s is not an element of this graph." % obj)
        return obj
      else:
        # We give up!
        raise TypeError("Can not convert a %s into a %s." %
                        (type(obj).__name__, types_str))
  
    def get_operations(self):
      """Return the list of operations in the graph.
  
      You can modify the operations in place, but modifications
      to the list such as inserts/delete have no effect on the
      list of operations known to the graph.
  
      This method may be called concurrently from multiple threads.
  
      Returns:
        A list of Operations.
      """
      if self._finalized:
        return list(self._nodes_by_id.values())
  
      with self._lock:
        return list(self._nodes_by_id.values())
  
    def get_operation_by_name(self, name):
      """Returns the `Operation` with the given `name`.
  
      This method may be called concurrently from multiple threads.
  
      Args:
        name: The name of the `Operation` to return.
  
      Returns:
        The `Operation` with the given `name`.
  
      Raises:
        TypeError: If `name` is not a string.
        KeyError: If `name` does not correspond to an operation in this graph.
      """
  
      if not isinstance(name, six.string_types):
        raise TypeError("Operation names are strings (or similar), not %s." %
                        type(name).__name__)
      return self.as_graph_element(name, allow_tensor=False, allow_operation=True)
  
    def _get_operation_by_name_unsafe(self, name):
      """Returns the `Operation` with the given `name`.
  
      This is a internal unsafe version of get_operation_by_name. It skips many
      checks and does not have user friendly error messages but runs considerably
      faster. This method may be called concurrently from multiple threads.
  
      Args:
        name: The name of the `Operation` to return.
  
      Returns:
        The `Operation` with the given `name`.
  
      Raises:
        KeyError: If `name` does not correspond to an operation in this graph.
      """
  
      if self._finalized:
        return self._nodes_by_name[name]
  
      with self._lock:
        return self._nodes_by_name[name]
  
    def _get_operation_by_tf_operation(self, tf_oper):
      op_name = pywrap_tf_session.TF_OperationName(tf_oper)
      return self._get_operation_by_name_unsafe(op_name)
  
    def get_tensor_by_name(self, name):
      """Returns the `Tensor` with the given `name`.
  
      This method may be called concurrently from multiple threads.
  
      Args:
        name: The name of the `Tensor` to return.
  
      Returns:
        The `Tensor` with the given `name`.
  
      Raises:
        TypeError: If `name` is not a string.
        KeyError: If `name` does not correspond to a tensor in this graph.
      """
      # Names should be strings.
      if not isinstance(name, six.string_types):
        raise TypeError("Tensor names are strings (or similar), not %s." %
                        type(name).__name__)
      return self.as_graph_element(name, allow_tensor=True, allow_operation=False)
  
    def _get_tensor_by_tf_output(self, tf_output):
      """Returns the `Tensor` representing `tf_output`.
  
      Note that there is only one such `Tensor`, i.e. multiple calls to this
      function with the same TF_Output value will always return the same `Tensor`
      object.
  
      Args:
        tf_output: A wrapped `TF_Output` (the C API equivalent of `Tensor`).
  
      Returns:
        The `Tensor` that represents `tf_output`.
      """
      op = self._get_operation_by_tf_operation(tf_output.oper)
      return op.outputs[tf_output.index]
  
    @property
    def _last_id(self):
      return self._next_id_counter
  
    def _get_op_def(self, type):  # pylint: disable=redefined-builtin
      """Returns the `OpDef` proto for `type`. `type` is a string."""
      # NOTE: No locking is required because the lookup and insertion operations
      # on Python dictionaries are atomic.
      try:
        return self._op_def_cache[type]
      except KeyError:
        with c_api_util.tf_buffer() as buf:
          # pylint: disable=protected-access
          pywrap_tf_session.TF_GraphGetOpDef(self._c_graph, compat.as_bytes(type),
                                             buf)
          # pylint: enable=protected-access
          data = pywrap_tf_session.TF_GetBuffer(buf)
        op_def = op_def_pb2.OpDef()
        op_def.ParseFromString(compat.as_bytes(data))
        self._op_def_cache[type] = op_def
        return op_def
  
    def as_default(self):
      """Returns a context manager that makes this `Graph` the default graph.
  
      This method should be used if you want to create multiple graphs
      in the same process. For convenience, a global default graph is
      provided, and all ops will be added to this graph if you do not
      create a new graph explicitly.
  
      Use this method with the `with` keyword to specify that ops created within
      the scope of a block should be added to this graph. In this case, once
      the scope of the `with` is exited, the previous default graph is set again
      as default. There is a stack, so it's ok to have multiple nested levels
      of `as_default` calls.
  
      The default graph is a property of the current thread. If you
      create a new thread, and wish to use the default graph in that
      thread, you must explicitly add a `with g.as_default():` in that
      thread's function.
  
      The following code examples are equivalent:
  
      ```python
      # 1. Using Graph.as_default():
      g = tf.Graph()
      with g.as_default():
        c = tf.constant(5.0)
        assert c.graph is g
  
      # 2. Constructing and making default:
      with tf.Graph().as_default() as g:
        c = tf.constant(5.0)
        assert c.graph is g
      ```
  
      If eager execution is enabled ops created under this context manager will be
      added to the graph instead of executed eagerly.
  
      Returns:
        A context manager for using this graph as the default graph.
      """
      return _default_graph_stack.get_controller(self)
  
    @property
    def collections(self):
      """Returns the names of the collections known to this graph."""
      return list(self._collections)
  
    def add_to_collection(self, name, value):
      """Stores `value` in the collection with the given `name`.
  
      Note that collections are not sets, so it is possible to add a value to
      a collection several times.
  
      Args:
        name: The key for the collection. The `GraphKeys` class contains many
          standard names for collections.
        value: The value to add to the collection.
      """  # pylint: disable=g-doc-exception
      self._check_not_finalized()
      with self._lock:
        if name not in self._collections:
          self._collections[name] = [value]
        else:
          self._collections[name].append(value)
  
    def add_to_collections(self, names, value):
      """Stores `value` in the collections given by `names`.
  
      Note that collections are not sets, so it is possible to add a value to
      a collection several times. This function makes sure that duplicates in
      `names` are ignored, but it will not check for pre-existing membership of
      `value` in any of the collections in `names`.
  
      `names` can be any iterable, but if `names` is a string, it is treated as a
      single collection name.
  
      Args:
        names: The keys for the collections to add to. The `GraphKeys` class
          contains many standard names for collections.
        value: The value to add to the collections.
      """
      # Make sure names are unique, but treat strings as a single collection name
      names = (names,) if isinstance(names, six.string_types) else set(names)
      for name in names:
        self.add_to_collection(name, value)
  
    def get_collection_ref(self, name):
      """Returns a list of values in the collection with the given `name`.
  
      If the collection exists, this returns the list itself, which can
      be modified in place to change the collection.  If the collection does
      not exist, it is created as an empty list and the list is returned.
  
      This is different from `get_collection()` which always returns a copy of
      the collection list if it exists and never creates an empty collection.
  
      Args:
        name: The key for the collection. For example, the `GraphKeys` class
          contains many standard names for collections.
  
      Returns:
        The list of values in the collection with the given `name`, or an empty
        list if no value has been added to that collection.
      """  # pylint: disable=g-doc-exception
      with self._lock:
        coll_list = self._collections.get(name, None)
        if coll_list is None:
          coll_list = []
          self._collections[name] = coll_list
        return coll_list
  
    def get_collection(self, name, scope=None):
      """Returns a list of values in the collection with the given `name`.
  
      This is different from `get_collection_ref()` which always returns the
      actual collection list if it exists in that it returns a new list each time
      it is called.
  
      Args:
        name: The key for the collection. For example, the `GraphKeys` class
          contains many standard names for collections.
        scope: (Optional.) A string. If supplied, the resulting list is filtered
          to include only items whose `name` attribute matches `scope` using
          `re.match`. Items without a `name` attribute are never returned if a
          scope is supplied. The choice of `re.match` means that a `scope` without
          special tokens filters by prefix.
  
      Returns:
        The list of values in the collection with the given `name`, or
        an empty list if no value has been added to that collection. The
        list contains the values in the order under which they were
        collected.
      """  # pylint: disable=g-doc-exception
      with self._lock:
        collection = self._collections.get(name, None)
        if collection is None:
          return []
        if scope is None:
          return list(collection)
        else:
          c = []
          regex = re.compile(scope)
          for item in collection:
            try:
              if regex.match(item.name):
                c.append(item)
            except AttributeError:
              # Collection items with no name are ignored.
              pass
          return c
  
    def get_all_collection_keys(self):
      """Returns a list of collections used in this graph."""
      with self._lock:
        return [x for x in self._collections if isinstance(x, six.string_types)]
  
    def clear_collection(self, name):
      """Clears all values in a collection.
  
      Args:
        name: The key for the collection. The `GraphKeys` class contains many
          standard names for collections.
      """
      self._check_not_finalized()
      with self._lock:
        if name in self._collections:
          del self._collections[name]
  
    @tf_contextlib.contextmanager
    def _original_op(self, op):
      """Python 'with' handler to help annotate ops with their originator.
  
      An op may have an 'original_op' property that indicates the op on which
      it was based. For example a replica op is based on the op that was
      replicated and a gradient op is based on the op that was differentiated.
  
      All ops created in the scope of this 'with' handler will have
      the given 'op' as their original op.
  
      Args:
        op: The Operation that all ops created in this scope will have as their
          original op.
  
      Yields:
        Nothing.
      """
      old_original_op = self._default_original_op
      self._default_original_op = op
      try:
        yield
      finally:
        self._default_original_op = old_original_op
  
    @property
    def _name_stack(self):
      # This may be called from a thread where name_stack doesn't yet exist.
      if not hasattr(self._thread_local, "_name_stack"):
        self._thread_local._name_stack = ""
      return self._thread_local._name_stack
  
    @_name_stack.setter
    def _name_stack(self, name_stack):
      self._thread_local._name_stack = name_stack
  
    # pylint: disable=g-doc-return-or-yield,line-too-long
    @tf_contextlib.contextmanager
    def name_scope(self, name):
      """Returns a context manager that creates hierarchical names for operations.
  
      A graph maintains a stack of name scopes. A `with name_scope(...):`
      statement pushes a new name onto the stack for the lifetime of the context.
  
      The `name` argument will be interpreted as follows:
  
      * A string (not ending with '/') will create a new name scope, in which
        `name` is appended to the prefix of all operations created in the
        context. If `name` has been used before, it will be made unique by
        calling `self.unique_name(name)`.
      * A scope previously captured from a `with g.name_scope(...) as
        scope:` statement will be treated as an "absolute" name scope, which
        makes it possible to re-enter existing scopes.
      * A value of `None` or the empty string will reset the current name scope
        to the top-level (empty) name scope.
  
      For example:
  
      ```python
      with tf.Graph().as_default() as g:
        c = tf.constant(5.0, name="c")
        assert c.op.name == "c"
        c_1 = tf.constant(6.0, name="c")
        assert c_1.op.name == "c_1"
  
        # Creates a scope called "nested"
        with g.name_scope("nested") as scope:
          nested_c = tf.constant(10.0, name="c")
          assert nested_c.op.name == "nested/c"
  
          # Creates a nested scope called "inner".
          with g.name_scope("inner"):
            nested_inner_c = tf.constant(20.0, name="c")
            assert nested_inner_c.op.name == "nested/inner/c"
  
          # Create a nested scope called "inner_1".
          with g.name_scope("inner"):
            nested_inner_1_c = tf.constant(30.0, name="c")
            assert nested_inner_1_c.op.name == "nested/inner_1/c"
  
            # Treats `scope` as an absolute name scope, and
            # switches to the "nested/" scope.
            with g.name_scope(scope):
              nested_d = tf.constant(40.0, name="d")
              assert nested_d.op.name == "nested/d"
  
              with g.name_scope(""):
                e = tf.constant(50.0, name="e")
                assert e.op.name == "e"
      ```
  
      The name of the scope itself can be captured by `with
      g.name_scope(...) as scope:`, which stores the name of the scope
      in the variable `scope`. This value can be used to name an
      operation that represents the overall result of executing the ops
      in a scope. For example:
  
      ```python
      inputs = tf.constant(...)
      with g.name_scope('my_layer') as scope:
        weights = tf.Variable(..., name="weights")
        biases = tf.Variable(..., name="biases")
        affine = tf.matmul(inputs, weights) + biases
        output = tf.nn.relu(affine, name=scope)
      ```
  
      NOTE: This constructor validates the given `name`. Valid scope
      names match one of the following regular expressions:
  
          [A-Za-z0-9.][A-Za-z0-9_.\\-/]* (for scopes at the root)
          [A-Za-z0-9_.\\-/]* (for other scopes)
  
      Args:
        name: A name for the scope.
  
      Returns:
        A context manager that installs `name` as a new name scope.
  
      Raises:
        ValueError: If `name` is not a valid scope name, according to the rules
          above.
      """
      if name:
        if isinstance(name, compat.bytes_or_text_types):
          name = compat.as_str(name)
  
        if self._name_stack:
          # Scopes created in a nested scope may have initial characters
          # that are illegal as the initial character of an op name
          # (viz. '-', '\', '/', and '_').
          if not _VALID_SCOPE_NAME_REGEX.match(name):
            raise ValueError("'%s' is not a valid scope name" % name)
        else:
          # Scopes created in the root must match the more restrictive
          # op name regex, which constrains the initial character.
          if not _VALID_OP_NAME_REGEX.match(name):
            raise ValueError("'%s' is not a valid scope name" % name)
      old_stack = self._name_stack
      if not name:  # Both for name=None and name="" we re-set to empty scope.
        new_stack = None
      elif name[-1] == "/":
        new_stack = name_from_scope_name(name)
      else:
        new_stack = self.unique_name(name)
      self._name_stack = new_stack
      try:
        yield "" if new_stack is None else new_stack + "/"
      finally:
        self._name_stack = old_stack
  
    # pylint: enable=g-doc-return-or-yield,line-too-long
  
    def unique_name(self, name, mark_as_used=True):
      """Return a unique operation name for `name`.
  
      Note: You rarely need to call `unique_name()` directly.  Most of
      the time you just need to create `with g.name_scope()` blocks to
      generate structured names.
  
      `unique_name` is used to generate structured names, separated by
      `"/"`, to help identify operations when debugging a graph.
      Operation names are displayed in error messages reported by the
      TensorFlow runtime, and in various visualization tools such as
      TensorBoard.
  
      If `mark_as_used` is set to `True`, which is the default, a new
      unique name is created and marked as in use. If it's set to `False`,
      the unique name is returned without actually being marked as used.
      This is useful when the caller simply wants to know what the name
      to be created will be.
  
      Args:
        name: The name for an operation.
        mark_as_used: Whether to mark this name as being used.
  
      Returns:
        A string to be passed to `create_op()` that will be used
        to name the operation being created.
      """
      if self._name_stack:
        name = self._name_stack + "/" + name
  
      # For the sake of checking for names in use, we treat names as case
      # insensitive (e.g. foo = Foo).
      name_key = name.lower()
      i = self._names_in_use.get(name_key, 0)
      # Increment the number for "name_key".
      if mark_as_used:
        self._names_in_use[name_key] = i + 1
      if i > 0:
        base_name_key = name_key
        # Make sure the composed name key is not already used.
        while name_key in self._names_in_use:
          name_key = "%s_%d" % (base_name_key, i)
          i += 1
        # Mark the composed name_key as used in case someone wants
        # to call unique_name("name_1").
        if mark_as_used:
          self._names_in_use[name_key] = 1
  
        # Return the new name with the original capitalization of the given name.
        name = "%s_%d" % (name, i - 1)
      return name
  
    def get_name_scope(self):
      """Returns the current name scope.
  
      For example:
  
      ```python
      with tf.name_scope('scope1'):
        with tf.name_scope('scope2'):
          print(tf.compat.v1.get_default_graph().get_name_scope())
      ```
      would print the string `scope1/scope2`.
  
      Returns:
        A string representing the current name scope.
      """
      return self._name_stack
  
    @tf_contextlib.contextmanager
    def _colocate_with_for_gradient(self, op, gradient_uid,
                                    ignore_existing=False):
      with self.colocate_with(op, ignore_existing):
        if gradient_uid is not None and self._control_flow_context is not None:
          self._control_flow_context.EnterGradientColocation(op, gradient_uid)
          try:
            yield
          finally:
            self._control_flow_context.ExitGradientColocation(op, gradient_uid)
        else:
          yield
  
    @tf_contextlib.contextmanager
    def colocate_with(self, op, ignore_existing=False):
      """Returns a context manager that specifies an op to colocate with.
  
      Note: this function is not for public use, only for internal libraries.
  
      For example:
  
      ```python
      a = tf.Variable([1.0])
      with g.colocate_with(a):
        b = tf.constant(1.0)
        c = tf.add(a, b)
      ```
  
      `b` and `c` will always be colocated with `a`, no matter where `a`
      is eventually placed.
  
      **NOTE** Using a colocation scope resets any existing device constraints.
  
      If `op` is `None` then `ignore_existing` must be `True` and the new
      scope resets all colocation and device constraints.
  
      Args:
        op: The op to colocate all created ops with, or `None`.
        ignore_existing: If true, only applies colocation of this op within the
          context, rather than applying all colocation properties on the stack.
          If `op` is `None`, this value must be `True`.
  
      Raises:
        ValueError: if op is None but ignore_existing is False.
  
      Yields:
        A context manager that specifies the op with which to colocate
        newly created ops.
      """
      if op is None and not ignore_existing:
        raise ValueError("Trying to reset colocation (op is None) but "
                         "ignore_existing is not True")
      op = _op_to_colocate_with(op, self)
  
      # By default, colocate_with resets the device function stack,
      # since colocate_with is typically used in specific internal
      # library functions where colocation is intended to be "stronger"
      # than device functions.
      #
      # In the future, a caller may specify that device_functions win
      # over colocation, in which case we can add support.
      device_fn_tmp = self._device_function_stack
      self._device_function_stack = traceable_stack.TraceableStack()
  
      if ignore_existing:
        current_stack = self._colocation_stack
        self._colocation_stack = traceable_stack.TraceableStack()
  
      if op is not None:
        # offset refers to the stack frame used for storing code location.
        # We use 4, the sum of 1 to use our caller's stack frame and 3
        # to jump over layers of context managers above us.
        self._colocation_stack.push_obj(op, offset=4)
  
      try:
        yield
      finally:
        # Restore device function stack
        self._device_function_stack = device_fn_tmp
        if op is not None:
          self._colocation_stack.pop_obj()
  
        # Reset the colocation stack if requested.
        if ignore_existing:
          self._colocation_stack = current_stack
  
    def _add_device_to_stack(self, device_name_or_function, offset=0):
      """Add device to stack manually, separate from a context manager."""
      total_offset = 1 + offset
      spec = _UserDeviceSpec(device_name_or_function)
      self._device_function_stack.push_obj(spec, offset=total_offset)
      return spec
  
    @tf_contextlib.contextmanager
    def device(self, device_name_or_function):
      # pylint: disable=line-too-long
      """Returns a context manager that specifies the default device to use.
  
      The `device_name_or_function` argument may either be a device name
      string, a device function, or None:
  
      * If it is a device name string, all operations constructed in
        this context will be assigned to the device with that name, unless
        overridden by a nested `device()` context.
      * If it is a function, it will be treated as a function from
        Operation objects to device name strings, and invoked each time
        a new Operation is created. The Operation will be assigned to
        the device with the returned name.
      * If it is None, all `device()` invocations from the enclosing context
        will be ignored.
  
      For information about the valid syntax of device name strings, see
      the documentation in
      [`DeviceNameUtils`](https://www.tensorflow.org/code/tensorflow/core/util/device_name_utils.h).
  
      For example:
  
      ```python
      with g.device('/device:GPU:0'):
        # All operations constructed in this context will be placed
        # on GPU 0.
        with g.device(None):
          # All operations constructed in this context will have no
          # assigned device.
  
      # Defines a function from `Operation` to device string.
      def matmul_on_gpu(n):
        if n.type == "MatMul":
          return "/device:GPU:0"
        else:
          return "/cpu:0"
  
      with g.device(matmul_on_gpu):
        # All operations of type "MatMul" constructed in this context
        # will be placed on GPU 0; all other operations will be placed
        # on CPU 0.
      ```
  
      **N.B.** The device scope may be overridden by op wrappers or
      other library code. For example, a variable assignment op
      `v.assign()` must be colocated with the `tf.Variable` `v`, and
      incompatible device scopes will be ignored.
  
      Args:
        device_name_or_function: The device name or function to use in the
          context.
  
      Yields:
        A context manager that specifies the default device to use for newly
        created ops.
  
      Raises:
        RuntimeError: If device scopes are not properly nested.
      """
      self._add_device_to_stack(device_name_or_function, offset=2)
      old_top_of_stack = self._device_function_stack.peek_top_obj()
      try:
        yield
      finally:
        new_top_of_stack = self._device_function_stack.peek_top_obj()
        if old_top_of_stack is not new_top_of_stack:
          raise RuntimeError("Exiting device scope without proper scope nesting.")
        self._device_function_stack.pop_obj()
  
    def _apply_device_functions(self, op):
      """Applies the current device function stack to the given operation."""
      # Apply any device functions in LIFO order, so that the most recently
      # pushed function has the first chance to apply a device to the op.
      # We apply here because the result can depend on the Operation's
      # signature, which is computed in the Operation constructor.
      # pylint: disable=protected-access
      prior_device_string = None
      for device_spec in self._device_function_stack.peek_objs():
        if device_spec.is_null_merge:
          continue
  
        if device_spec.function is None:
          break
  
        device_string = device_spec.string_merge(op)
  
        # Take advantage of the fact that None is a singleton and Python interns
        # strings, since identity checks are faster than equality checks.
        if device_string is not prior_device_string:
          op._set_device_from_string(device_string)
          prior_device_string = device_string
      op._device_code_locations = self._snapshot_device_function_stack_metadata()
      # pylint: enable=protected-access
  
    # pylint: disable=g-doc-return-or-yield
    @tf_contextlib.contextmanager
    def container(self, container_name):
      """Returns a context manager that specifies the resource container to use.
  
      Stateful operations, such as variables and queues, can maintain their
      states on devices so that they can be shared by multiple processes.
      A resource container is a string name under which these stateful
      operations are tracked. These resources can be released or cleared
      with `tf.Session.reset()`.
  
      For example:
  
      ```python
      with g.container('experiment0'):
        # All stateful Operations constructed in this context will be placed
        # in resource container "experiment0".
        v1 = tf.Variable([1.0])
        v2 = tf.Variable([2.0])
        with g.container("experiment1"):
          # All stateful Operations constructed in this context will be
          # placed in resource container "experiment1".
          v3 = tf.Variable([3.0])
          q1 = tf.queue.FIFOQueue(10, tf.float32)
        # All stateful Operations constructed in this context will be
        # be created in the "experiment0".
        v4 = tf.Variable([4.0])
        q1 = tf.queue.FIFOQueue(20, tf.float32)
        with g.container(""):
          # All stateful Operations constructed in this context will be
          # be placed in the default resource container.
          v5 = tf.Variable([5.0])
          q3 = tf.queue.FIFOQueue(30, tf.float32)
  
      # Resets container "experiment0", after which the state of v1, v2, v4, q1
      # will become undefined (such as uninitialized).
      tf.Session.reset(target, ["experiment0"])
      ```
  
      Args:
        container_name: container name string.
  
      Returns:
        A context manager for defining resource containers for stateful ops,
          yields the container name.
      """
      original_container = self._container
      self._container = container_name
      try:
        yield self._container
      finally:
        self._container = original_container
  
    # pylint: enable=g-doc-return-or-yield
  
    class _ControlDependenciesController(object):
      """Context manager for `control_dependencies()`."""
  
      def __init__(self, graph, control_inputs):
        """Create a new `_ControlDependenciesController`.
  
        A `_ControlDependenciesController` is the context manager for
        `with tf.control_dependencies()` blocks.  These normally nest,
        as described in the documentation for `control_dependencies()`.
  
        The `control_inputs` argument list control dependencies that must be
        added to the current set of control dependencies.  Because of
        uniquification the set can be empty even if the caller passed a list of
        ops.  The special value `None` indicates that we want to start a new
        empty set of control dependencies instead of extending the current set.
  
        In that case we also clear the current control flow context, which is an
        additional mechanism to add control dependencies.
  
        Args:
          graph: The graph that this controller is managing.
          control_inputs: List of ops to use as control inputs in addition to the
            current control dependencies.  None to indicate that the dependencies
            should be cleared.
        """
        self._graph = graph
        if control_inputs is None:
          self._control_inputs_val = []
          self._new_stack = True
        else:
          self._control_inputs_val = control_inputs
          self._new_stack = False
        self._seen_nodes = set()
        self._old_stack = None
        self._old_control_flow_context = None
  
  # pylint: disable=protected-access
  
      def __enter__(self):
        if self._new_stack:
          # Clear the control_dependencies graph.
          self._old_stack = self._graph._control_dependencies_stack
          self._graph._control_dependencies_stack = []
          # Clear the control_flow_context too.
          self._old_control_flow_context = self._graph._get_control_flow_context()
          self._graph._set_control_flow_context(None)
        self._graph._push_control_dependencies_controller(self)
  
      def __exit__(self, unused_type, unused_value, unused_traceback):
        self._graph._pop_control_dependencies_controller(self)
        if self._new_stack:
          self._graph._control_dependencies_stack = self._old_stack
          self._graph._set_control_flow_context(self._old_control_flow_context)
  
  # pylint: enable=protected-access
  
      @property
      def control_inputs(self):
        return self._control_inputs_val
  
      def add_op(self, op):
        if isinstance(op, Tensor):
          op = op.ref()
        self._seen_nodes.add(op)
  
      def op_in_group(self, op):
        if isinstance(op, Tensor):
          op = op.ref()
        return op in self._seen_nodes
  
    def _push_control_dependencies_controller(self, controller):
      self._control_dependencies_stack.append(controller)
  
    def _pop_control_dependencies_controller(self, controller):
      assert self._control_dependencies_stack[-1] is controller
      self._control_dependencies_stack.pop()
  
    def _current_control_dependencies(self):
      ret = set()
      for controller in self._control_dependencies_stack:
        for op in controller.control_inputs:
          ret.add(op)
      return ret
  
    def _control_dependencies_for_inputs(self, input_ops):
      """For an op that takes `input_ops` as inputs, compute control inputs.
  
      The returned control dependencies should yield an execution that
      is equivalent to adding all control inputs in
      self._control_dependencies_stack to a newly created op. However,
      this function attempts to prune the returned control dependencies
      by observing that nodes created within the same `with
      control_dependencies(...):` block may have data dependencies that make
      the explicit approach redundant.
  
      Args:
        input_ops: The data input ops for an op to be created.
  
      Returns:
        A list of control inputs for the op to be created.
      """
      ret = []
      for controller in self._control_dependencies_stack:
        # If any of the input_ops already depends on the inputs from controller,
        # we say that the new op is dominated (by that input), and we therefore
        # do not need to add control dependencies for this controller's inputs.
        dominated = False
        for op in input_ops:
          if controller.op_in_group(op):
            dominated = True
            break
        if not dominated:
          # Don't add a control input if we already have a data dependency on i.
          # NOTE(mrry): We do not currently track transitive data dependencies,
          #   so we may add redundant control inputs.
          ret.extend(c for c in controller.control_inputs if c not in input_ops)
      return ret
  
    def _record_op_seen_by_control_dependencies(self, op):
      """Record that the given op depends on all registered control dependencies.
  
      Args:
        op: An Operation.
      """
      for controller in self._control_dependencies_stack:
        controller.add_op(op)
  
    def control_dependencies(self, control_inputs):
      """Returns a context manager that specifies control dependencies.
  
      Use with the `with` keyword to specify that all operations constructed
      within the context should have control dependencies on
      `control_inputs`. For example:
  
      ```python
      with g.control_dependencies([a, b, c]):
        # `d` and `e` will only run after `a`, `b`, and `c` have executed.
        d = ...
        e = ...
      ```
  
      Multiple calls to `control_dependencies()` can be nested, and in
      that case a new `Operation` will have control dependencies on the union
      of `control_inputs` from all active contexts.
  
      ```python
      with g.control_dependencies([a, b]):
        # Ops constructed here run after `a` and `b`.
        with g.control_dependencies([c, d]):
          # Ops constructed here run after `a`, `b`, `c`, and `d`.
      ```
  
      You can pass None to clear the control dependencies:
  
      ```python
      with g.control_dependencies([a, b]):
        # Ops constructed here run after `a` and `b`.
        with g.control_dependencies(None):
          # Ops constructed here run normally, not waiting for either `a` or `b`.
          with g.control_dependencies([c, d]):
            # Ops constructed here run after `c` and `d`, also not waiting
            # for either `a` or `b`.
      ```
  
      *N.B.* The control dependencies context applies *only* to ops that
      are constructed within the context. Merely using an op or tensor
      in the context does not add a control dependency. The following
      example illustrates this point:
  
      ```python
      # WRONG
      def my_func(pred, tensor):
        t = tf.matmul(tensor, tensor)
        with tf.control_dependencies([pred]):
          # The matmul op is created outside the context, so no control
          # dependency will be added.
          return t
  
      # RIGHT
      def my_func(pred, tensor):
        with tf.control_dependencies([pred]):
          # The matmul op is created in the context, so a control dependency
          # will be added.
          return tf.matmul(tensor, tensor)
      ```
  
      Also note that though execution of ops created under this scope will trigger
      execution of the dependencies, the ops created under this scope might still
      be pruned from a normal tensorflow graph. For example, in the following
      snippet of code the dependencies are never executed:
  
      ```python
        loss = model.loss()
        with tf.control_dependencies(dependencies):
          loss = loss + tf.constant(1)  # note: dependencies ignored in the
                                        # backward pass
        return tf.gradients(loss, model.variables)
      ```
  
      This is because evaluating the gradient graph does not require evaluating
      the constant(1) op created in the forward pass.
  
      Args:
        control_inputs: A list of `Operation` or `Tensor` objects which must be
          executed or computed before running the operations defined in the
          context.  Can also be `None` to clear the control dependencies.
  
      Returns:
       A context manager that specifies control dependencies for all
       operations constructed within the context.
  
      Raises:
        TypeError: If `control_inputs` is not a list of `Operation` or
          `Tensor` objects.
      """
      if control_inputs is None:
        return self._ControlDependenciesController(self, None)
      # First convert the inputs to ops, and deduplicate them.
      # NOTE(mrry): Other than deduplication, we do not currently track direct
      #   or indirect dependencies between control_inputs, which may result in
      #   redundant control inputs.
      control_ops = []
      current = self._current_control_dependencies()
      for c in control_inputs:
        # The hasattr(handle) is designed to match ResourceVariables. This is so
        # control dependencies on a variable or on an unread variable don't
        # trigger reads.
        if (isinstance(c, IndexedSlices) or
            (hasattr(c, "_handle") and hasattr(c, "op"))):
          c = c.op
        c = self.as_graph_element(c)
        if isinstance(c, Tensor):
          c = c.op
        elif not isinstance(c, Operation):
          raise TypeError("Control input must be Operation or Tensor: %s" % c)
        if c not in current:
          control_ops.append(c)
          current.add(c)
      return self._ControlDependenciesController(self, control_ops)
  
    # pylint: disable=g-doc-return-or-yield
    @tf_contextlib.contextmanager
    def _attr_scope(self, attr_map):
      """EXPERIMENTAL: A context manager for setting attributes on operators.
  
      This context manager can be used to add additional
      attributes to operators within the scope of the context.
  
      For example:
  
         with ops.Graph().as_default() as g:
           f_1 = Foo()  # No extra attributes
           with g._attr_scope({"_a": tf.attr_value_pb2.AttrValue(b=False)}):
             f_2 = Foo()  # Additional attribute _a=False
             with g._attr_scope({"_a": tf.attr_value_pb2.AttrValue(b=True)}):
               f_3 = Foo()  # Additional attribute _a=False
               with g._attr_scope({"_a": None}):
                 f_4 = Foo()  # No additional attributes.
  
      Args:
        attr_map: A dictionary mapping attr name strings to AttrValue protocol
          buffers or None.
  
      Returns:
        A context manager that sets the kernel label to be used for one or more
        ops created in that context.
  
      Raises:
        TypeError: If attr_map is not a dictionary mapping
          strings to AttrValue protobufs.
      """
      if not isinstance(attr_map, dict):
        raise TypeError("attr_map must be a dictionary mapping "
                        "strings to AttrValue protocol buffers")
      # The saved_attrs dictionary stores any currently-set labels that
      # will be overridden by this context manager.
      saved_attrs = {}
      # Install the given attribute
      for name, attr in attr_map.items():
        if not (isinstance(name, six.string_types) and
                (isinstance(attr, (type(None), attr_value_pb2.AttrValue)) or
                 callable(attr))):
          raise TypeError("attr_map must be a dictionary mapping "
                          "strings to AttrValue protocol buffers or "
                          "callables that emit AttrValue protocol buffers")
        try:
          saved_attrs[name] = self._attr_scope_map[name]
        except KeyError:
          pass
        if attr is None:
          del self._attr_scope_map[name]
        else:
          self._attr_scope_map[name] = attr
      try:
        yield  # The code within the context runs here.
      finally:
        # Remove the attributes set for this context, and restore any saved
        # attributes.
        for name, attr in attr_map.items():
          try:
            self._attr_scope_map[name] = saved_attrs[name]
          except KeyError:
            del self._attr_scope_map[name]
  
    # pylint: enable=g-doc-return-or-yield
  
    # pylint: disable=g-doc-return-or-yield
    @tf_contextlib.contextmanager
    def _kernel_label_map(self, op_to_kernel_label_map):
      """EXPERIMENTAL: A context manager for setting kernel labels.
  
      This context manager can be used to select particular
      implementations of kernels within the scope of the context.
  
      For example:
  
          with ops.Graph().as_default() as g:
            f_1 = Foo()  # Uses the default registered kernel for the Foo op.
            with g.kernel_label_map({"Foo": "v_2"}):
              f_2 = Foo()  # Uses the registered kernel with label "v_2"
                           # for the Foo op.
              with g.kernel_label_map({"Foo": "v_3"}):
                f_3 = Foo()  # Uses the registered kernel with label "v_3"
                             # for the Foo op.
                with g.kernel_label_map({"Foo": ""}):
                  f_4 = Foo()  # Uses the default registered kernel
                               # for the Foo op.
  
      Args:
        op_to_kernel_label_map: A dictionary mapping op type strings to kernel
          label strings.
  
      Returns:
        A context manager that sets the kernel label to be used for one or more
        ops created in that context.
  
      Raises:
        TypeError: If op_to_kernel_label_map is not a dictionary mapping
          strings to strings.
      """
      if not isinstance(op_to_kernel_label_map, dict):
        raise TypeError("op_to_kernel_label_map must be a dictionary mapping "
                        "strings to strings")
      # The saved_labels dictionary stores any currently-set labels that
      # will be overridden by this context manager.
      saved_labels = {}
      # Install the given label
      for op_type, label in op_to_kernel_label_map.items():
        if not (isinstance(op_type, six.string_types) and
                isinstance(label, six.string_types)):
          raise TypeError("op_to_kernel_label_map must be a dictionary mapping "
                          "strings to strings")
        try:
          saved_labels[op_type] = self._op_to_kernel_label_map[op_type]
        except KeyError:
          pass
        self._op_to_kernel_label_map[op_type] = label
      try:
        yield  # The code within the context runs here.
      finally:
        # Remove the labels set for this context, and restore any saved labels.
        for op_type, label in op_to_kernel_label_map.items():
          try:
            self._op_to_kernel_label_map[op_type] = saved_labels[op_type]
          except KeyError:
            del self._op_to_kernel_label_map[op_type]
  
    # pylint: enable=g-doc-return-or-yield
  
    @tf_contextlib.contextmanager
    def _override_gradient_function(self, gradient_function_map):
      """Specify gradient function for the given op type."""
  
      # This is an internal API and we don't need nested context for this.
      assert not self._gradient_function_map
      self._gradient_function_map = gradient_function_map
      yield
      self._gradient_function_map = {}
  
    # pylint: disable=g-doc-return-or-yield
    @tf_contextlib.contextmanager
    def gradient_override_map(self, op_type_map):
      """EXPERIMENTAL: A context manager for overriding gradient functions.
  
      This context manager can be used to override the gradient function
      that will be used for ops within the scope of the context.
  
      For example:
  
      ```python
      @tf.RegisterGradient("CustomSquare")
      def _custom_square_grad(op, grad):
        # ...
  
      with tf.Graph().as_default() as g:
        c = tf.constant(5.0)
        s_1 = tf.square(c)  # Uses the default gradient for tf.square.
        with g.gradient_override_map({"Square": "CustomSquare"}):
          s_2 = tf.square(s_2)  # Uses _custom_square_grad to compute the
                                # gradient of s_2.
      ```
  
      Args:
        op_type_map: A dictionary mapping op type strings to alternative op type
          strings.
  
      Returns:
        A context manager that sets the alternative op type to be used for one
        or more ops created in that context.
  
      Raises:
        TypeError: If `op_type_map` is not a dictionary mapping strings to
          strings.
      """
      if not isinstance(op_type_map, dict):
        raise TypeError("op_type_map must be a dictionary mapping "
                        "strings to strings")
      # The saved_mappings dictionary stores any currently-set mappings that
      # will be overridden by this context manager.
      saved_mappings = {}
      # Install the given label
      for op_type, mapped_op_type in op_type_map.items():
        if not (isinstance(op_type, six.string_types) and
                isinstance(mapped_op_type, six.string_types)):
          raise TypeError("op_type_map must be a dictionary mapping "
                          "strings to strings")
        try:
          saved_mappings[op_type] = self._gradient_override_map[op_type]
        except KeyError:
          pass
        self._gradient_override_map[op_type] = mapped_op_type
      try:
        yield  # The code within the context runs here.
      finally:
        # Remove the labels set for this context, and restore any saved labels.
        for op_type, mapped_op_type in op_type_map.items():
          try:
            self._gradient_override_map[op_type] = saved_mappings[op_type]
          except KeyError:
            del self._gradient_override_map[op_type]
  
    # pylint: enable=g-doc-return-or-yield
  
    def prevent_feeding(self, tensor):
      """Marks the given `tensor` as unfeedable in this graph."""
      self._unfeedable_tensors.add(tensor)
  
    def is_feedable(self, tensor):
      """Returns `True` if and only if `tensor` is feedable."""
      return tensor not in self._unfeedable_tensors
  
    def prevent_fetching(self, op):
      """Marks the given `op` as unfetchable in this graph."""
      self._unfetchable_ops.add(op)
  
    def is_fetchable(self, tensor_or_op):
      """Returns `True` if and only if `tensor_or_op` is fetchable."""
      if isinstance(tensor_or_op, Tensor):
        return tensor_or_op.op not in self._unfetchable_ops
      else:
        return tensor_or_op not in self._unfetchable_ops
  
    def switch_to_thread_local(self):
      """Make device, colocation and dependencies stacks thread-local.
  
      Device, colocation and dependencies stacks are not thread-local be default.
      If multiple threads access them, then the state is shared.  This means that
      one thread may affect the behavior of another thread.
  
      After this method is called, the stacks become thread-local.  If multiple
      threads access them, then the state is not shared.  Each thread uses its own
      value; a thread doesn't affect other threads by mutating such a stack.
  
      The initial value for every thread's stack is set to the current value
      of the stack when `switch_to_thread_local()` was first called.
      """
      if not self._stack_state_is_thread_local:
        self._stack_state_is_thread_local = True
  
    @property
    def _device_function_stack(self):
      if self._stack_state_is_thread_local:
        # This may be called from a thread where device_function_stack doesn't yet
        # exist.
        # pylint: disable=protected-access
        if not hasattr(self._thread_local, "_device_function_stack"):
          stack_copy_for_this_thread = self._graph_device_function_stack.copy()
          self._thread_local._device_function_stack = stack_copy_for_this_thread
        return self._thread_local._device_function_stack
        # pylint: enable=protected-access
      else:
        return self._graph_device_function_stack
  
    @property
    def _device_functions_outer_to_inner(self):
      user_device_specs = self._device_function_stack.peek_objs()
      device_functions = [spec.function for spec in user_device_specs]
      device_functions_outer_to_inner = list(reversed(device_functions))
      return device_functions_outer_to_inner
  
    def _snapshot_device_function_stack_metadata(self):
      """Return device function stack as a list of TraceableObjects.
  
      Returns:
        [traceable_stack.TraceableObject, ...] where each TraceableObject's .obj
        member is a displayable name for the user's argument to Graph.device, and
        the filename and lineno members point to the code location where
        Graph.device was called directly or indirectly by the user.
      """
      snapshot = []
      for obj in self._device_function_stack.peek_traceable_objs():
        obj_copy = obj.copy_metadata()
        obj_copy.obj = obj.obj.display_name
        snapshot.append(obj_copy)
      return snapshot
  
    @_device_function_stack.setter
    def _device_function_stack(self, device_function_stack):
      if self._stack_state_is_thread_local:
        # pylint: disable=protected-access
        self._thread_local._device_function_stack = device_function_stack
        # pylint: enable=protected-access
      else:
        self._graph_device_function_stack = device_function_stack
  
    @property
    def _colocation_stack(self):
      """Return thread-local copy of colocation stack."""
      if self._stack_state_is_thread_local:
        # This may be called from a thread where colocation_stack doesn't yet
        # exist.
        # pylint: disable=protected-access
        if not hasattr(self._thread_local, "_colocation_stack"):
          stack_copy_for_this_thread = self._graph_colocation_stack.copy()
          self._thread_local._colocation_stack = stack_copy_for_this_thread
        return self._thread_local._colocation_stack
        # pylint: enable=protected-access
      else:
        return self._graph_colocation_stack
  
    def _snapshot_colocation_stack_metadata(self):
      """Return colocation stack metadata as a dictionary."""
      return {
          traceable_obj.obj.name: traceable_obj.copy_metadata()
          for traceable_obj in self._colocation_stack.peek_traceable_objs()
      }
  
    @_colocation_stack.setter
    def _colocation_stack(self, colocation_stack):
      if self._stack_state_is_thread_local:
        # pylint: disable=protected-access
        self._thread_local._colocation_stack = colocation_stack
        # pylint: enable=protected-access
      else:
        self._graph_colocation_stack = colocation_stack
  
    @property
    def _control_dependencies_stack(self):
      if self._stack_state_is_thread_local:
        # This may be called from a thread where control_dependencies_stack
        # doesn't yet exist.
        if not hasattr(self._thread_local, "_control_dependencies_stack"):
          self._thread_local._control_dependencies_stack = (
              self._graph_control_dependencies_stack[:])
        return self._thread_local._control_dependencies_stack
      else:
        return self._graph_control_dependencies_stack
  
    @_control_dependencies_stack.setter
    def _control_dependencies_stack(self, control_dependencies):
      if self._stack_state_is_thread_local:
        self._thread_local._control_dependencies_stack = control_dependencies
      else:
        self._graph_control_dependencies_stack = control_dependencies
  
    @property
    def _distribution_strategy_stack(self):
      """A stack to maintain distribution strategy context for each thread."""
      if not hasattr(self._thread_local, "_distribution_strategy_stack"):
        self._thread_local._distribution_strategy_stack = []  # pylint: disable=protected-access
      return self._thread_local._distribution_strategy_stack  # pylint: disable=protected-access
  
    @_distribution_strategy_stack.setter
    def _distribution_strategy_stack(self, _distribution_strategy_stack):
      self._thread_local._distribution_strategy_stack = (  # pylint: disable=protected-access
          _distribution_strategy_stack)
  
    @property
    def _global_distribute_strategy_scope(self):
      """For implementing `tf.distribute.set_strategy()`."""
      if not hasattr(self._thread_local, "distribute_strategy_scope"):
        self._thread_local.distribute_strategy_scope = None
      return self._thread_local.distribute_strategy_scope
  
    @_global_distribute_strategy_scope.setter
    def _global_distribute_strategy_scope(self, distribute_strategy_scope):
      self._thread_local.distribute_strategy_scope = (distribute_strategy_scope)
  
    @property
    def _auto_cast_variable_read_dtype(self):
      """The dtype that instances of `AutoCastVariable` will be casted to.
  
      This is None if `AutoCastVariables` should not be casted.
  
      See `AutoCastVariable` for more information.
  
      Returns:
        The dtype that instances of `AutoCastVariable` will be casted to.
      """
      if not hasattr(self._thread_local, "_auto_cast_variable_read_dtype"):
        self._thread_local._auto_cast_variable_read_dtype = None  # pylint: disable=protected-access
      return self._thread_local._auto_cast_variable_read_dtype  # pylint: disable=protected-access
  
    @_auto_cast_variable_read_dtype.setter
    def _auto_cast_variable_read_dtype(self, dtype):
      if dtype:
        dtype = dtypes.as_dtype(dtype)
      self._thread_local._auto_cast_variable_read_dtype = dtype  # pylint: disable=protected-access
  
    @tf_contextlib.contextmanager
    def _enable_auto_casting_variables(self, dtype):
      """Context manager to automatically cast AutoCastVariables.
  
      If an AutoCastVariable `var` is used under this context manager, it will be
      casted to `dtype` before being used.
  
      See `AutoCastVariable` for more information.
  
      Args:
        dtype: The dtype that AutoCastVariables should be casted to.
  
      Yields:
        Nothing.
      """
      prev_read_dtype = self._auto_cast_variable_read_dtype
      try:
        self._auto_cast_variable_read_dtype = dtype
        yield
      finally:
        self._auto_cast_variable_read_dtype = prev_read_dtype
  
    def _mutation_lock(self):
      """Returns a lock to guard code that creates & mutates ops.
  
      See the comment for self._group_lock for more info.
      """
      return self._group_lock.group(_MUTATION_LOCK_GROUP)
  
    def _session_run_lock(self):
      """Returns a lock to guard code for Session.run.
  
      See the comment for self._group_lock for more info.
      """
      return self._group_lock.group(_SESSION_RUN_LOCK_GROUP)
  
  
  # TODO(agarwal): currently device directives in an outer eager scope will not
  # apply to inner graph mode code. Fix that.
  
  
  @tf_export(v1=["device"])
  def device(device_name_or_function):
    """Wrapper for `Graph.device()` using the default graph.
  
    See `tf.Graph.device` for more details.
  
    Args:
      device_name_or_function: The device name or function to use in the context.
  
    Returns:
      A context manager that specifies the default device to use for newly
      created ops.
  
    Raises:
      RuntimeError: If eager execution is enabled and a function is passed in.
    """
    if context.executing_eagerly():
      if callable(device_name_or_function):
        raise RuntimeError(
            "tf.device does not support functions when eager execution "
            "is enabled.")
      return context.device(device_name_or_function)
    elif executing_eagerly_outside_functions():
      @tf_contextlib.contextmanager
      def combined(device_name_or_function):
        with get_default_graph().device(device_name_or_function):
          if not callable(device_name_or_function):
            with context.device(device_name_or_function):
              yield
          else:
            yield
      return combined(device_name_or_function)
    else:
      return get_default_graph().device(device_name_or_function)
  
  
  @tf_export("device", v1=[])
  def device_v2(device_name):
    """Specifies the device for ops created/executed in this context.
  
    This function specifies the device to be used for ops created/executed in a
    particular context. Nested contexts will inherit and also create/execute
    their ops on the specified device. If a specific device is not required,
    consider not using this function so that a device can be automatically
    assigned.  In general the use of this function is optional. `device_name` can
    be fully specified, as in "/job:worker/task:1/device:cpu:0", or partially
    specified, containing only a subset of the "/"-separated fields. Any fields
    which are specified will override device annotations from outer scopes.
  
    For example:
  
    ```python
    with tf.device('/job:foo'):
      # ops created here have devices with /job:foo
      with tf.device('/job:bar/task:0/device:gpu:2'):
        # ops created here have the fully specified device above
      with tf.device('/device:gpu:1'):
        # ops created here have the device '/job:foo/device:gpu:1'
    ```
  
    Args:
      device_name: The device name to use in the context.
  
    Returns:
      A context manager that specifies the default device to use for newly
      created ops.
  
    Raises:
      RuntimeError: If a function is passed in.
    """
    if callable(device_name):
      raise RuntimeError("tf.device does not support functions.")
    return device(device_name)
  
  
  @tf_export(v1=["container"])
  def container(container_name):
    """Wrapper for `Graph.container()` using the default graph.
  
    Args:
      container_name: The container string to use in the context.
  
    Returns:
      A context manager that specifies the default container to use for newly
      created stateful ops.
    """
    return get_default_graph().container(container_name)
  
  
  def _colocate_with_for_gradient(op, gradient_uid, ignore_existing=False):
    if context.executing_eagerly():
      if op is not None:
        if not hasattr(op, "device"):
          op = internal_convert_to_tensor_or_indexed_slices(op)
        return device(op.device)
      else:
        return NullContextmanager()
    else:
      default_graph = get_default_graph()
      if isinstance(op, EagerTensor):
        if default_graph.building_function:
          return default_graph.device(op.device)
        else:
          raise ValueError("Encountered an Eager-defined Tensor during graph "
                           "construction, but a function was not being built.")
      return default_graph._colocate_with_for_gradient(
          op, gradient_uid=gradient_uid, ignore_existing=ignore_existing)
  
  
  # Internal interface to colocate_with. colocate_with has been deprecated from
  # public API. There are still a few internal uses of colocate_with. Add internal
  # only API for those uses to avoid deprecation warning.
  def colocate_with(op, ignore_existing=False):
    return _colocate_with_for_gradient(op, None, ignore_existing=ignore_existing)
  
  
  @deprecation.deprecated(
      date=None, instructions="Colocations handled automatically by placer.")
  @tf_export(v1=["colocate_with"])
  def _colocate_with(op, ignore_existing=False):
    return colocate_with(op, ignore_existing)
  
  
  @tf_export("control_dependencies")
  def control_dependencies(control_inputs):
    """Wrapper for `Graph.control_dependencies()` using the default graph.
  
    See `tf.Graph.control_dependencies`
    for more details.
  
    When eager execution is enabled, any callable object in the `control_inputs`
    list will be called.
  
    Args:
      control_inputs: A list of `Operation` or `Tensor` objects which must be
        executed or computed before running the operations defined in the context.
        Can also be `None` to clear the control dependencies. If eager execution
        is enabled, any callable object in the `control_inputs` list will be
        called.
  
    Returns:
     A context manager that specifies control dependencies for all
     operations constructed within the context.
    """
    if context.executing_eagerly():
      if control_inputs:
        # Execute any pending callables.
        for control in control_inputs:
          if callable(control):
            control()
      return NullContextmanager()
    else:
      return get_default_graph().control_dependencies(control_inputs)
  
  
  class _DefaultStack(threading.local):
    """A thread-local stack of objects for providing implicit defaults."""
  
    def __init__(self):
      super(_DefaultStack, self).__init__()
      self._enforce_nesting = True
      self.stack = []
  
    def get_default(self):
      return self.stack[-1] if len(self.stack) >= 1 else None
  
    def reset(self):
      self.stack = []
  
    def is_cleared(self):
      return not self.stack
  
    @property
    def enforce_nesting(self):
      return self._enforce_nesting
  
    @enforce_nesting.setter
    def enforce_nesting(self, value):
      self._enforce_nesting = value
  
    @tf_contextlib.contextmanager
    def get_controller(self, default):
      """A context manager for manipulating a default stack."""
      self.stack.append(default)
      try:
        yield default
      finally:
        # stack may be empty if reset() was called
        if self.stack:
          if self._enforce_nesting:
            if self.stack[-1] is not default:
              raise AssertionError(
                  "Nesting violated for default stack of %s objects" %
                  type(default))
            self.stack.pop()
          else:
            self.stack.remove(default)
  
  
  _default_session_stack = _DefaultStack()  # pylint: disable=protected-access
  
  
  def default_session(session):
    """Python "with" handler for defining a default session.
  
    This function provides a means of registering a session for handling
    Tensor.eval() and Operation.run() calls. It is primarily intended for use
    by session.Session, but can be used with any object that implements
    the Session.run() interface.
  
    Use with the "with" keyword to specify that Tensor.eval() and Operation.run()
    invocations within the scope of a block should be executed by a particular
    session.
  
    The default session applies to the current thread only, so it is always
    possible to inspect the call stack and determine the scope of a default
    session. If you create a new thread, and wish to use the default session
    in that thread, you must explicitly add a "with ops.default_session(sess):"
    block in that thread's function.
  
    Example:
      The following code examples are equivalent:
  
      # 1. Using the Session object directly:
      sess = ...
      c = tf.constant(5.0)
      sess.run(c)
  
      # 2. Using default_session():
      sess = ...
      with ops.default_session(sess):
        c = tf.constant(5.0)
        result = c.eval()
  
      # 3. Overriding default_session():
      sess = ...
      with ops.default_session(sess):
        c = tf.constant(5.0)
        with ops.default_session(...):
          c.eval(session=sess)
  
    Args:
      session: The session to be installed as the default session.
  
    Returns:
      A context manager for the default session.
    """
    return _default_session_stack.get_controller(session)
  
  
  @tf_export(v1=["get_default_session"])
  def get_default_session():
    """Returns the default session for the current thread.
  
    The returned `Session` will be the innermost session on which a
    `Session` or `Session.as_default()` context has been entered.
  
    NOTE: The default session is a property of the current thread. If you
    create a new thread, and wish to use the default session in that
    thread, you must explicitly add a `with sess.as_default():` in that
    thread's function.
  
    Returns:
      The default `Session` being used in the current thread.
    """
    return _default_session_stack.get_default()
  
  
  def _eval_using_default_session(tensors, feed_dict, graph, session=None):
    """Uses the default session to evaluate one or more tensors.
  
    Args:
      tensors: A single Tensor, or a list of Tensor objects.
      feed_dict: A dictionary that maps Tensor objects (or tensor names) to lists,
        numpy ndarrays, TensorProtos, or strings.
      graph: The graph in which the tensors are defined.
      session: (Optional) A different session to use to evaluate "tensors".
  
    Returns:
      Either a single numpy ndarray if "tensors" is a single tensor; or a list
      of numpy ndarrays that each correspond to the respective element in
      "tensors".
  
    Raises:
      ValueError: If no default session is available; the default session
        does not have "graph" as its graph; or if "session" is specified,
        and it does not have "graph" as its graph.
    """
    if session is None:
      session = get_default_session()
      if session is None:
        raise ValueError("Cannot evaluate tensor using `eval()`: No default "
                         "session is registered. Use `with "
                         "sess.as_default()` or pass an explicit session to "
                         "`eval(session=sess)`")
      if session.graph is not graph:
        raise ValueError("Cannot use the default session to evaluate tensor: "
                         "the tensor's graph is different from the session's "
                         "graph. Pass an explicit session to "
                         "`eval(session=sess)`.")
    else:
      if session.graph is not graph:
        raise ValueError("Cannot use the given session to evaluate tensor: "
                         "the tensor's graph is different from the session's "
                         "graph.")
    return session.run(tensors, feed_dict)
  
  
  def _run_using_default_session(operation, feed_dict, graph, session=None):
    """Uses the default session to run "operation".
  
    Args:
      operation: The Operation to be run.
      feed_dict: A dictionary that maps Tensor objects (or tensor names) to lists,
        numpy ndarrays, TensorProtos, or strings.
      graph: The graph in which "operation" is defined.
      session: (Optional) A different session to use to run "operation".
  
    Raises:
      ValueError: If no default session is available; the default session
        does not have "graph" as its graph; or if "session" is specified,
        and it does not have "graph" as its graph.
    """
    if session is None:
      session = get_default_session()
      if session is None:
        raise ValueError("Cannot execute operation using `run()`: No default "
                         "session is registered. Use `with "
                         "sess.as_default():` or pass an explicit session to "
                         "`run(session=sess)`")
      if session.graph is not graph:
        raise ValueError("Cannot use the default session to execute operation: "
                         "the operation's graph is different from the "
                         "session's graph. Pass an explicit session to "
                         "run(session=sess).")
    else:
      if session.graph is not graph:
        raise ValueError("Cannot use the given session to execute operation: "
                         "the operation's graph is different from the session's "
                         "graph.")
    session.run(operation, feed_dict)
  
  
  class _DefaultGraphStack(_DefaultStack):  # pylint: disable=protected-access
    """A thread-local stack of objects for providing an implicit default graph."""
  
    def __init__(self):
      super(_DefaultGraphStack, self).__init__()
      self._global_default_graph = None
  
    def get_default(self):
      """Override that returns a global default if the stack is empty."""
      ret = super(_DefaultGraphStack, self).get_default()
      if ret is None:
        ret = self._GetGlobalDefaultGraph()
      return ret
  
    def _GetGlobalDefaultGraph(self):
      if self._global_default_graph is None:
        # TODO(mrry): Perhaps log that the default graph is being used, or set
        #   provide some other feedback to prevent confusion when a mixture of
        #   the global default graph and an explicit graph are combined in the
        #   same process.
        self._global_default_graph = Graph()
      return self._global_default_graph
  
    def reset(self):
      super(_DefaultGraphStack, self).reset()
      self._global_default_graph = None
  
    @tf_contextlib.contextmanager
    def get_controller(self, default):
      context.context().context_switches.push(default.building_function,
                                              default.as_default,
                                              default._device_function_stack)
      try:
        with super(_DefaultGraphStack,
                   self).get_controller(default) as g, context.graph_mode():
          yield g
      finally:
        # If an exception is raised here it may be hiding a related exception in
        # the try-block (just above).
        context.context().context_switches.pop()
  
  
  _default_graph_stack = _DefaultGraphStack()
  
  
  # Shared helper used in init_scope and executing_eagerly_outside_functions
  # to obtain the outermost context that is not building a function, and the
  # innermost non empty device stack.
  def _get_outer_context_and_inner_device_stack():
    """Get the outermost context not building a function."""
    default_graph = get_default_graph()
    outer_context = None
    innermost_nonempty_device_stack = default_graph._device_function_stack  # pylint: disable=protected-access
  
    if not _default_graph_stack.stack:
      # If the default graph stack is empty, then we cannot be building a
      # function. Install the global graph (which, in this case, is also the
      # default graph) as the outer context.
      if default_graph.building_function:
        raise RuntimeError("The global graph is building a function.")
      outer_context = default_graph.as_default
    else:
      # Find a context that is not building a function.
      for stack_entry in reversed(context.context().context_switches.stack):
        if not innermost_nonempty_device_stack:
          innermost_nonempty_device_stack = stack_entry.device_stack
        if not stack_entry.is_building_function:
          outer_context = stack_entry.enter_context_fn
          break
  
      if outer_context is None:
        # As a last resort, obtain the global default graph; this graph doesn't
        # necessarily live on the graph stack (and hence it doesn't necessarily
        # live on the context stack), but it is stored in the graph stack's
        # encapsulating object.
        outer_context = _default_graph_stack._GetGlobalDefaultGraph().as_default  # pylint: disable=protected-access
  
    if outer_context is None:
      # Sanity check; this shouldn't be triggered.
      raise RuntimeError("All graphs are building functions, and no "
                         "eager context was previously active.")
  
    return outer_context, innermost_nonempty_device_stack
  
  
  # pylint: disable=g-doc-return-or-yield,line-too-long
  @tf_export("init_scope")
  @tf_contextlib.contextmanager
  def init_scope():
    """A context manager that lifts ops out of control-flow scopes and function-building graphs.
  
    There is often a need to lift variable initialization ops out of control-flow
    scopes, function-building graphs, and gradient tapes. Entering an
    `init_scope` is a mechanism for satisfying these desiderata. In particular,
    entering an `init_scope` has three effects:
  
      (1) All control dependencies are cleared the moment the scope is entered;
          this is equivalent to entering the context manager returned from
          `control_dependencies(None)`, which has the side-effect of exiting
          control-flow scopes like `tf.cond` and `tf.while_loop`.
  
      (2) All operations that are created while the scope is active are lifted
          into the lowest context on the `context_stack` that is not building a
          graph function. Here, a context is defined as either a graph or an eager
          context. Every context switch, i.e., every installation of a graph as
          the default graph and every switch into eager mode, is logged in a
          thread-local stack called `context_switches`; the log entry for a
          context switch is popped from the stack when the context is exited.
          Entering an `init_scope` is equivalent to crawling up
          `context_switches`, finding the first context that is not building a
          graph function, and entering it. A caveat is that if graph mode is
          enabled but the default graph stack is empty, then entering an
          `init_scope` will simply install a fresh graph as the default one.
  
      (3) The gradient tape is paused while the scope is active.
  
    When eager execution is enabled, code inside an init_scope block runs with
    eager execution enabled even when tracing a `tf.function`. For example:
  
    ```python
    tf.compat.v1.enable_eager_execution()
  
    @tf.function
    def func():
      # A function constructs TensorFlow graphs,
      # it does not execute eagerly.
      assert not tf.executing_eagerly()
      with tf.init_scope():
        # Initialization runs with eager execution enabled
        assert tf.executing_eagerly()
    ```
  
    Raises:
      RuntimeError: if graph state is incompatible with this initialization.
    """
    # pylint: enable=g-doc-return-or-yield,line-too-long
  
    if context.executing_eagerly():
      # Fastpath.
      with tape.stop_recording():
        yield
    else:
      # Retrieve the active name scope: entering an `init_scope` preserves
      # the name scope of the current context.
      scope = get_default_graph().get_name_scope()
      if scope and scope[-1] != "/":
        # Names that end with trailing slashes are treated by `name_scope` as
        # absolute.
        scope = scope + "/"
  
      outer_context, innermost_nonempty_device_stack = (
          _get_outer_context_and_inner_device_stack())
  
      outer_graph = None
      outer_device_stack = None
      try:
        with outer_context(), name_scope(
            scope, skip_on_eager=False), control_dependencies(
                None), tape.stop_recording():
          context_manager = NullContextmanager
          context_manager_input = None
          if not context.executing_eagerly():
            # The device stack is preserved when lifting into a graph. Eager
            # execution doesn't implement device stacks and in particular it
            # doesn't support device functions, so in general it's not possible
            # to do the same when lifting into the eager context.
            outer_graph = get_default_graph()
            outer_device_stack = outer_graph._device_function_stack  # pylint: disable=protected-access
            outer_graph._device_function_stack = innermost_nonempty_device_stack  # pylint: disable=protected-access
          elif innermost_nonempty_device_stack is not None:
            for device_spec in innermost_nonempty_device_stack.peek_objs():
              if device_spec.function is None:
                break
              if device_spec.raw_string:
                context_manager = context.device
                context_manager_input = device_spec.raw_string
                break
              # It is currently not possible to have a device function in V2,
              # but in V1 we are unable to apply device functions in eager mode.
              # This means that we will silently skip some of the entries on the
              # device stack in V1 + eager mode.
  
          with context_manager(context_manager_input):
            yield
      finally:
        # If an exception is raised here it may be hiding a related exception in
        # try-block (just above).
        if outer_graph is not None:
          outer_graph._device_function_stack = outer_device_stack  # pylint: disable=protected-access
  
  
  @tf_export(v1=["executing_eagerly_outside_functions"])
  def executing_eagerly_outside_functions():
    """Returns True if executing eagerly, even if inside a graph function.
  
    This function will check the outermost context for the program and see if
    it is in eager mode. It is useful comparing to `tf.executing_eagerly()`,
    which checks the current context and will return `False` within a
    `tf.function` body. It can be used to build library that behave differently
    in eager runtime and v1 session runtime (deprecated).
  
    Example:
  
    >>> tf.compat.v1.enable_eager_execution()
    >>> @tf.function
    ... def func():
    ...   # A function constructs TensorFlow graphs, it does not execute eagerly,
    ...   # but the outer most context is still eager.
    ...   assert not tf.executing_eagerly()
    ...   return tf.compat.v1.executing_eagerly_outside_functions()
    >>> func()
    <tf.Tensor: shape=(), dtype=bool, numpy=True>
  
    Returns:
      boolean, whether the outermost context is in eager mode.
    """
    if context.executing_eagerly():
      return True
    else:
      outer_context, _ = _get_outer_context_and_inner_device_stack()
      with outer_context():
        return context.executing_eagerly()
  
  
  def inside_function():
    return get_default_graph().building_function
  
  
  @tf_export(v1=["enable_eager_execution"])
  def enable_eager_execution(config=None, device_policy=None,
                             execution_mode=None):
    """Enables eager execution for the lifetime of this program.
  
    Eager execution provides an imperative interface to TensorFlow. With eager
    execution enabled, TensorFlow functions execute operations immediately (as
    opposed to adding to a graph to be executed later in a `tf.compat.v1.Session`)
    and
    return concrete values (as opposed to symbolic references to a node in a
    computational graph).
  
    For example:
  
    ```python
    tf.compat.v1.enable_eager_execution()
  
    # After eager execution is enabled, operations are executed as they are
    # defined and Tensor objects hold concrete values, which can be accessed as
    # numpy.ndarray`s through the numpy() method.
    assert tf.multiply(6, 7).numpy() == 42
    ```
  
    Eager execution cannot be enabled after TensorFlow APIs have been used to
    create or execute graphs. It is typically recommended to invoke this function
    at program startup and not in a library (as most libraries should be usable
    both with and without eager execution).
  
    Args:
      config: (Optional.) A `tf.compat.v1.ConfigProto` to use to configure the
        environment in which operations are executed. Note that
        `tf.compat.v1.ConfigProto` is also used to configure graph execution (via
        `tf.compat.v1.Session`) and many options within `tf.compat.v1.ConfigProto`
        are not implemented (or are irrelevant) when eager execution is enabled.
      device_policy: (Optional.) Policy controlling how operations requiring
        inputs on a specific device (e.g., a GPU 0) handle inputs on a different
        device  (e.g. GPU 1 or CPU). When set to None, an appropriate value will
        be picked automatically. The value picked may change between TensorFlow
        releases.
        Valid values:
        - tf.contrib.eager.DEVICE_PLACEMENT_EXPLICIT: raises an error if the
          placement is not correct.
        - tf.contrib.eager.DEVICE_PLACEMENT_WARN: copies the tensors which are not
          on the right device but logs a warning.
        - tf.contrib.eager.DEVICE_PLACEMENT_SILENT: silently copies the tensors.
          Note that this may hide performance problems as there is no notification
          provided when operations are blocked on the tensor being copied between
          devices.
        - tf.contrib.eager.DEVICE_PLACEMENT_SILENT_FOR_INT32: silently copies
          int32 tensors, raising errors on the other ones.
      execution_mode: (Optional.) Policy controlling how operations dispatched are
        actually executed. When set to None, an appropriate value will be picked
        automatically. The value picked may change between TensorFlow releases.
        Valid values:
        - tf.contrib.eager.SYNC: executes each operation synchronously.
        - tf.contrib.eager.ASYNC: executes each operation asynchronously. These
          operations may return "non-ready" handles.
  
    Raises:
      ValueError: If eager execution is enabled after creating/executing a
       TensorFlow graph, or if options provided conflict with a previous call
       to this function.
    """
    _api_usage_gauge.get_cell().set(True)
    if context.default_execution_mode != context.EAGER_MODE:
      return enable_eager_execution_internal(
          config=config,
          device_policy=device_policy,
          execution_mode=execution_mode,
          server_def=None)
  
  
  @tf_export(v1=["disable_eager_execution"])
  def disable_eager_execution():
    """Disables eager execution.
  
    This function can only be called before any Graphs, Ops, or Tensors have been
    created. It can be used at the beginning of the program for complex migration
    projects from TensorFlow 1.x to 2.x.
    """
    _api_usage_gauge.get_cell().set(False)
    context.default_execution_mode = context.GRAPH_MODE
    c = context.context_safe()
    if c is not None:
      c._thread_local_data.is_eager = False  # pylint: disable=protected-access
  
  
  def enable_eager_execution_internal(config=None,
                                      device_policy=None,
                                      execution_mode=None,
                                      server_def=None):
    """Enables eager execution for the lifetime of this program.
  
    Most of the doc string for enable_eager_execution is relevant here as well.
  
    Args:
      config: See enable_eager_execution doc string
      device_policy: See enable_eager_execution doc string
      execution_mode: See enable_eager_execution doc string
      server_def: (Optional.) A tensorflow::ServerDef proto. Enables execution on
        remote devices. GrpcServers need to be started by creating an identical
        server_def to this, and setting the appropriate task_indexes, so that the
        servers can communicate. It will then be possible to execute operations on
        remote devices.
  
    Raises:
      ValueError
  
    """
    if config is not None and not isinstance(config, config_pb2.ConfigProto):
      raise TypeError("config must be a tf.ConfigProto, but got %s" %
                      type(config))
    if device_policy not in (None, context.DEVICE_PLACEMENT_EXPLICIT,
                             context.DEVICE_PLACEMENT_WARN,
                             context.DEVICE_PLACEMENT_SILENT,
                             context.DEVICE_PLACEMENT_SILENT_FOR_INT32):
      raise ValueError(
          "device_policy must be one of None, tf.contrib.eager.DEVICE_PLACEMENT_*"
      )
    if execution_mode not in (None, context.SYNC, context.ASYNC):
      raise ValueError(
          "execution_mode must be one of None, tf.contrib.eager.SYNC, "
          "tf.contrib.eager.ASYNC")
    if context.default_execution_mode == context.GRAPH_MODE:
      graph_mode_has_been_used = (
          _default_graph_stack._global_default_graph is not None)  # pylint: disable=protected-access
      if graph_mode_has_been_used:
        raise ValueError(
            "tf.enable_eager_execution must be called at program startup.")
    context.default_execution_mode = context.EAGER_MODE
    # pylint: disable=protected-access
    with context._context_lock:
      if context._context is None:
        context._set_context_locked(context.Context(
            config=config,
            device_policy=device_policy,
            execution_mode=execution_mode,
            server_def=server_def))
      elif ((config is not None and config is not context._context._config) or
            (device_policy is not None and
             device_policy is not context._context._device_policy) or
            (execution_mode is not None and
             execution_mode is not context._context._execution_mode)):
        raise ValueError(
            "Trying to change the options of an active eager"
            " execution. Context config: %s, specified config:"
            " %s. Context device policy: %s, specified device"
            " policy: %s. Context execution mode: %s, "
            " specified execution mode %s." %
            (context._context._config, config, context._context._device_policy,
             device_policy, context._context._execution_mode, execution_mode))
      else:
        # We already created everything, so update the thread local data.
        context._context._thread_local_data.is_eager = True
  
    # Monkey patch to get rid of an unnecessary conditional since the context is
    # now initialized.
    context.context = context.context_safe
  
  
  def eager_run(main=None, argv=None):
    """Runs the program with an optional main function and argv list.
  
    The program will run with eager execution enabled.
  
    Example:
    ```python
    import tensorflow as tf
    # Import subject to future changes:
    from tensorflow.contrib.eager.python import tfe
  
    def main(_):
      u = tf.constant(6.0)
      v = tf.constant(7.0)
      print(u * v)
  
    if __name__ == "__main__":
      tfe.run()
    ```
  
    Args:
      main: the main function to run.
      argv: the arguments to pass to it.
    """
    enable_eager_execution()
    app.run(main, argv)
  
  
  @tf_export(v1=["reset_default_graph"])
  def reset_default_graph():
    """Clears the default graph stack and resets the global default graph.
  
    NOTE: The default graph is a property of the current thread. This
    function applies only to the current thread.  Calling this function while
    a `tf.compat.v1.Session` or `tf.compat.v1.InteractiveSession` is active will
    result in undefined
    behavior. Using any previously created `tf.Operation` or `tf.Tensor` objects
    after calling this function will result in undefined behavior.
    Raises:
      AssertionError: If this function is called within a nested graph.
    """
    if not _default_graph_stack.is_cleared():
      raise AssertionError("Do not use tf.reset_default_graph() to clear "
                           "nested graphs. If you need a cleared graph, "
                           "exit the nesting and create a new graph.")
    _default_graph_stack.reset()
  
  
  @tf_export(v1=["get_default_graph"])
  def get_default_graph():
    """Returns the default graph for the current thread.
  
    The returned graph will be the innermost graph on which a
    `Graph.as_default()` context has been entered, or a global default
    graph if none has been explicitly created.
  
    NOTE: The default graph is a property of the current thread. If you
    create a new thread, and wish to use the default graph in that
    thread, you must explicitly add a `with g.as_default():` in that
    thread's function.
  
    Returns:
      The default `Graph` being used in the current thread.
    """
    return _default_graph_stack.get_default()
  
  
  def has_default_graph():
    """Returns True if there is a default graph."""
    return len(_default_graph_stack.stack) >= 1
  
  
  def get_name_scope():
    """Returns the current name scope in the default_graph.
  
    For example:
  
    ```python
    with tf.name_scope('scope1'):
      with tf.name_scope('scope2'):
        print(tf.get_name_scope())
    ```
    would print the string `scope1/scope2`.
  
    Returns:
      A string representing the current name scope.
    """
    if context.executing_eagerly():
      return context.context().scope_name.rstrip("/")
    return get_default_graph().get_name_scope()
  
  
  def _assert_same_graph(original_item, item):
    """Fail if the 2 items are from different graphs.
  
    Args:
      original_item: Original item to check against.
      item: Item to check.
  
    Raises:
      ValueError: if graphs do not match.
    """
    if original_item.graph is not item.graph:
      raise ValueError("%s must be from the same graph as %s." %
                       (item, original_item))
  
  
  def _get_graph_from_inputs(op_input_list, graph=None):
    """Returns the appropriate graph to use for the given inputs.
  
    This library method provides a consistent algorithm for choosing the graph
    in which an Operation should be constructed:
  
    1. If the default graph is being used to construct a function, we
       use the default graph.
    2. If the "graph" is specified explicitly, we validate that all of the inputs
       in "op_input_list" are compatible with that graph.
    3. Otherwise, we attempt to select a graph from the first Operation-
       or Tensor-valued input in "op_input_list", and validate that all other
       such inputs are in the same graph.
    4. If the graph was not specified and it could not be inferred from
       "op_input_list", we attempt to use the default graph.
  
    Args:
      op_input_list: A list of inputs to an operation, which may include `Tensor`,
        `Operation`, and other objects that may be converted to a graph element.
      graph: (Optional) The explicit graph to use.
  
    Raises:
      TypeError: If op_input_list is not a list or tuple, or if graph is not a
        Graph.
      ValueError: If a graph is explicitly passed and not all inputs are from it,
        or if the inputs are from multiple graphs, or we could not find a graph
        and there was no default graph.
  
    Returns:
      The appropriate graph to use for the given inputs.
  
    """
    current_default_graph = get_default_graph()
    if current_default_graph.building_function:
      return current_default_graph
  
    op_input_list = tuple(op_input_list)  # Handle generators correctly
    if graph and not isinstance(graph, Graph):
      raise TypeError("Input graph needs to be a Graph: %s" % graph)
  
    # 1. We validate that all of the inputs are from the same graph. This is
    #    either the supplied graph parameter, or the first one selected from one
    #    the graph-element-valued inputs. In the latter case, we hold onto
    #    that input in original_graph_element so we can provide a more
    #    informative error if a mismatch is found.
    original_graph_element = None
    for op_input in op_input_list:
      # Determine if this is a valid graph_element.
      # TODO(josh11b): Note that we exclude subclasses of Tensor. Need to clean this
      # up.
      graph_element = None
      if (isinstance(op_input, (Operation, _TensorLike)) and
          ((not isinstance(op_input, Tensor)) or type(op_input) == Tensor)):  # pylint: disable=unidiomatic-typecheck
        graph_element = op_input
      else:
        graph_element = _as_graph_element(op_input)
  
      if graph_element is not None:
        if not graph:
          original_graph_element = graph_element
          graph = graph_element.graph
        elif original_graph_element is not None:
          _assert_same_graph(original_graph_element, graph_element)
        elif graph_element.graph is not graph:
          raise ValueError("%s is not from the passed-in graph." % graph_element)
  
    # 2. If all else fails, we use the default graph, which is always there.
    return graph or current_default_graph
  
  
  @tf_export(v1=["GraphKeys"])
  class GraphKeys(object):
    """Standard names to use for graph collections.
  
    The standard library uses various well-known names to collect and
    retrieve values associated with a graph. For example, the
    `tf.Optimizer` subclasses default to optimizing the variables
    collected under `tf.GraphKeys.TRAINABLE_VARIABLES` if none is
    specified, but it is also possible to pass an explicit list of
    variables.
  
    The following standard keys are defined:
  
    * `GLOBAL_VARIABLES`: the default collection of `Variable` objects, shared
      across distributed environment (model variables are subset of these). See
      `tf.compat.v1.global_variables`
      for more details.
      Commonly, all `TRAINABLE_VARIABLES` variables will be in `MODEL_VARIABLES`,
      and all `MODEL_VARIABLES` variables will be in `GLOBAL_VARIABLES`.
    * `LOCAL_VARIABLES`: the subset of `Variable` objects that are local to each
      machine. Usually used for temporarily variables, like counters.
      Note: use `tf.contrib.framework.local_variable` to add to this collection.
    * `MODEL_VARIABLES`: the subset of `Variable` objects that are used in the
      model for inference (feed forward). Note: use
      `tf.contrib.framework.model_variable` to add to this collection.
    * `TRAINABLE_VARIABLES`: the subset of `Variable` objects that will
      be trained by an optimizer. See
      `tf.compat.v1.trainable_variables`
      for more details.
    * `SUMMARIES`: the summary `Tensor` objects that have been created in the
      graph. See
      `tf.compat.v1.summary.merge_all`
      for more details.
    * `QUEUE_RUNNERS`: the `QueueRunner` objects that are used to
      produce input for a computation. See
      `tf.compat.v1.train.start_queue_runners`
      for more details.
    * `MOVING_AVERAGE_VARIABLES`: the subset of `Variable` objects that will also
      keep moving averages.  See
      `tf.compat.v1.moving_average_variables`
      for more details.
    * `REGULARIZATION_LOSSES`: regularization losses collected during graph
      construction.
  
    The following standard keys are _defined_, but their collections are **not**
    automatically populated as many of the others are:
  
    * `WEIGHTS`
    * `BIASES`
    * `ACTIVATIONS`
    """
  
    # Key to collect Variable objects that are global (shared across machines).
    # Default collection for all variables, except local ones.
    GLOBAL_VARIABLES = "variables"
    # Key to collect local variables that are local to the machine and are not
    # saved/restored.
    LOCAL_VARIABLES = "local_variables"
    # Key to collect local variables which are used to accumulate interal state
    # to be used in tf.metrics.*.
    METRIC_VARIABLES = "metric_variables"
    # Key to collect model variables defined by layers.
    MODEL_VARIABLES = "model_variables"
    # Key to collect Variable objects that will be trained by the
    # optimizers.
    TRAINABLE_VARIABLES = "trainable_variables"
    # Key to collect summaries.
    SUMMARIES = "summaries"
    # Key to collect QueueRunners.
    QUEUE_RUNNERS = "queue_runners"
    # Key to collect table initializers.
    TABLE_INITIALIZERS = "table_initializer"
    # Key to collect asset filepaths. An asset represents an external resource
    # like a vocabulary file.
    ASSET_FILEPATHS = "asset_filepaths"
    # Key to collect Variable objects that keep moving averages.
    MOVING_AVERAGE_VARIABLES = "moving_average_variables"
    # Key to collect regularization losses at graph construction.
    REGULARIZATION_LOSSES = "regularization_losses"
    # Key to collect concatenated sharded variables.
    CONCATENATED_VARIABLES = "concatenated_variables"
    # Key to collect savers.
    SAVERS = "savers"
    # Key to collect weights
    WEIGHTS = "weights"
    # Key to collect biases
    BIASES = "biases"
    # Key to collect activations
    ACTIVATIONS = "activations"
    # Key to collect update_ops
    UPDATE_OPS = "update_ops"
    # Key to collect losses
    LOSSES = "losses"
    # Key to collect BaseSaverBuilder.SaveableObject instances for checkpointing.
    SAVEABLE_OBJECTS = "saveable_objects"
    # Key to collect all shared resources used by the graph which need to be
    # initialized once per cluster.
    RESOURCES = "resources"
    # Key to collect all shared resources used in this graph which need to be
    # initialized once per session.
    LOCAL_RESOURCES = "local_resources"
    # Trainable resource-style variables.
    TRAINABLE_RESOURCE_VARIABLES = "trainable_resource_variables"
  
    # Key to indicate various ops.
    INIT_OP = "init_op"
    LOCAL_INIT_OP = "local_init_op"
    READY_OP = "ready_op"
    READY_FOR_LOCAL_INIT_OP = "ready_for_local_init_op"
    SUMMARY_OP = "summary_op"
    GLOBAL_STEP = "global_step"
  
    # Used to count the number of evaluations performed during a single evaluation
    # run.
    EVAL_STEP = "eval_step"
    TRAIN_OP = "train_op"
  
    # Key for control flow context.
    COND_CONTEXT = "cond_context"
    WHILE_CONTEXT = "while_context"
  
    # Used to store v2 summary names.
    _SUMMARY_COLLECTION = "_SUMMARY_V2"
  
    # List of all collections that keep track of variables.
    _VARIABLE_COLLECTIONS = [
        GLOBAL_VARIABLES,
        LOCAL_VARIABLES,
        METRIC_VARIABLES,
        MODEL_VARIABLES,
        TRAINABLE_VARIABLES,
        MOVING_AVERAGE_VARIABLES,
        CONCATENATED_VARIABLES,
        TRAINABLE_RESOURCE_VARIABLES,
    ]
  
    # Key for streaming model ports.
    # NOTE(yuanbyu): internal and experimental.
    _STREAMING_MODEL_PORTS = "streaming_model_ports"
  
    @decorator_utils.classproperty
    @deprecation.deprecated(None, "Use `tf.GraphKeys.GLOBAL_VARIABLES` instead.")
    def VARIABLES(cls):  # pylint: disable=no-self-argument
      return cls.GLOBAL_VARIABLES
  
  
  def dismantle_graph(graph):
    """Cleans up reference cycles from a `Graph`.
  
    Helpful for making sure the garbage collector doesn't need to run after a
    temporary `Graph` is no longer needed.
  
    Args:
      graph: A `Graph` object to destroy. Neither it nor any of its ops are usable
        after this function runs.
    """
    memory.dismantle_ordered_dict(graph._functions)  # pylint: disable=protected-access
  
    # Now clean up Operation<->Graph reference cycles by clearing all of the
    # attributes for the Graph and its ops.
    graph_operations = graph.get_operations()
    for op in graph_operations:
      op.__dict__ = {}
    graph.__dict__ = {}
  
  
  @tf_export(v1=["add_to_collection"])
  def add_to_collection(name, value):
    """Wrapper for `Graph.add_to_collection()` using the default graph.
  
    See `tf.Graph.add_to_collection`
    for more details.
  
    Args:
      name: The key for the collection. For example, the `GraphKeys` class
        contains many standard names for collections.
      value: The value to add to the collection.  @compatibility(eager)
        Collections are only supported in eager when variables are created inside
        an EagerVariableStore (e.g. as part of a layer or template).
        @end_compatibility
    """
    get_default_graph().add_to_collection(name, value)
  
  
  @tf_export(v1=["add_to_collections"])
  def add_to_collections(names, value):
    """Wrapper for `Graph.add_to_collections()` using the default graph.
  
    See `tf.Graph.add_to_collections`
    for more details.
  
    Args:
      names: The key for the collections. The `GraphKeys` class contains many
        standard names for collections.
      value: The value to add to the collections.  @compatibility(eager)
        Collections are only supported in eager when variables are created inside
        an EagerVariableStore (e.g. as part of a layer or template).
        @end_compatibility
    """
    get_default_graph().add_to_collections(names, value)
  
  
  @tf_export(v1=["get_collection_ref"])
  def get_collection_ref(key):
    """Wrapper for `Graph.get_collection_ref()` using the default graph.
  
    See `tf.Graph.get_collection_ref`
    for more details.
  
    Args:
      key: The key for the collection. For example, the `GraphKeys` class contains
        many standard names for collections.
  
    Returns:
      The list of values in the collection with the given `name`, or an empty
      list if no value has been added to that collection.  Note that this returns
      the collection list itself, which can be modified in place to change the
      collection.
  
    @compatibility(eager)
    Collections are not supported when eager execution is enabled.
    @end_compatibility
    """
    return get_default_graph().get_collection_ref(key)
  
  
  @tf_export(v1=["get_collection"])
  def get_collection(key, scope=None):
    """Wrapper for `Graph.get_collection()` using the default graph.
  
    See `tf.Graph.get_collection`
    for more details.
  
    Args:
      key: The key for the collection. For example, the `GraphKeys` class contains
        many standard names for collections.
      scope: (Optional.) If supplied, the resulting list is filtered to include
        only items whose `name` attribute matches using `re.match`. Items without
        a `name` attribute are never returned if a scope is supplied and the
        choice or `re.match` means that a `scope` without special tokens filters
        by prefix.
  
    Returns:
      The list of values in the collection with the given `name`, or
      an empty list if no value has been added to that collection. The
      list contains the values in the order under which they were
      collected.
  
    @compatibility(eager)
    Collections are not supported when eager execution is enabled.
    @end_compatibility
    """
    return get_default_graph().get_collection(key, scope)
  
  
  def get_all_collection_keys():
    """Returns a list of collections used in the default graph."""
    return get_default_graph().get_all_collection_keys()
  
  
  def name_scope(name, default_name=None, values=None, skip_on_eager=True):
    """Internal-only entry point for `name_scope*`.
  
    Internal ops do not use the public API and instead rely on
    `ops.name_scope` regardless of the execution mode. This function
    dispatches to the correct `name_scope*` implementation based on
    the arguments provided and the current mode. Specifically,
  
    * if `values` contains a graph tensor `Graph.name_scope` is used;
    * `name_scope_v1` is used in graph mode;
    * `name_scope_v2` -- in eager mode.
  
    Args:
      name: The name argument that is passed to the op function.
      default_name: The default name to use if the `name` argument is `None`.
      values: The list of `Tensor` arguments that are passed to the op function.
      skip_on_eager: Indicates to return NullContextmanager if executing eagerly.
        By default this is True since naming tensors and operations in eager mode
        have little use and cause unnecessary performance overhead. However, it is
        important to preserve variable names since they are often useful for
        debugging and saved models.
  
    Returns:
      `name_scope*` context manager.
    """
    ctx = context.context()
    in_eager_mode = ctx.executing_eagerly()
    if not in_eager_mode:
      return internal_name_scope_v1(name, default_name, values)
  
    if skip_on_eager:
      return NullContextmanager()
  
    name = default_name if name is None else name
    if values:
      # The presence of a graph tensor in `values` overrides the context.
      # TODO(slebedev): this is Keras-specific and should be removed.
      # pylint: disable=unidiomatic-typecheck
      graph_value = next((value for value in values if type(value) == Tensor),
                         None)
      # pylint: enable=unidiomatic-typecheck
      if graph_value is not None:
        return graph_value.graph.name_scope(name)
  
    return name_scope_v2(name or "")
  
  
  class internal_name_scope_v1(object):  # pylint: disable=invalid-name
    """Graph-only version of `name_scope_v1`."""
  
    @property
    def name(self):
      return self._name
  
    def __init__(self, name, default_name=None, values=None):
      """Initialize the context manager.
  
      Args:
        name: The name argument that is passed to the op function.
        default_name: The default name to use if the `name` argument is `None`.
        values: The list of `Tensor` arguments that are passed to the op function.
  
      Raises:
        TypeError: if `default_name` is passed in but not a string.
      """
      if not (default_name is None or isinstance(default_name, six.string_types)):
        raise TypeError(
            "`default_name` type (%s) is not a string type. You likely meant to "
            "pass this into the `values` kwarg." % type(default_name))
      self._name = default_name if name is None else name
      self._default_name = default_name
      self._values = values
  
    def __enter__(self):
      """Start the scope block.
  
      Returns:
        The scope name.
  
      Raises:
        ValueError: if neither `name` nor `default_name` is provided
          but `values` are.
      """
      if self._name is None and self._values is not None:
        # We only raise an error if values is not None (provided) because
        # currently tf.name_scope(None) (values=None then) is sometimes used as
        # an idiom to reset to top scope.
        raise ValueError(
            "At least one of name (%s) and default_name (%s) must be provided."
            % (self._name, self._default_name))
  
      g = get_default_graph()
      if self._values and not g.building_function:
        # Specialize based on the knowledge that `_get_graph_from_inputs()`
        # ignores `inputs` when building a function.
        g_from_inputs = _get_graph_from_inputs(self._values)
        if g_from_inputs is not g:
          g = g_from_inputs
          self._g_manager = g.as_default()
          self._g_manager.__enter__()
        else:
          self._g_manager = None
      else:
        self._g_manager = None
  
      try:
        self._name_scope = g.name_scope(self._name)
        return self._name_scope.__enter__()
      except:
        if self._g_manager is not None:
          self._g_manager.__exit__(*sys.exc_info())
        raise
  
    def __exit__(self, *exc_info):
      self._name_scope.__exit__(*exc_info)
      if self._g_manager is not None:
        self._g_manager.__exit__(*exc_info)
  
  
  # Named like a function for backwards compatibility with the
  # @tf_contextlib.contextmanager version, which was switched to a class to avoid
  # some object creation overhead.
  @tf_export(v1=["name_scope"])
  class name_scope_v1(object):  # pylint: disable=invalid-name
    """A context manager for use when defining a Python op.
  
    This context manager validates that the given `values` are from the
    same graph, makes that graph the default graph, and pushes a
    name scope in that graph (see
    `tf.Graph.name_scope`
    for more details on that).
  
    For example, to define a new Python op called `my_op`:
  
    ```python
    def my_op(a, b, c, name=None):
      with tf.name_scope(name, "MyOp", [a, b, c]) as scope:
        a = tf.convert_to_tensor(a, name="a")
        b = tf.convert_to_tensor(b, name="b")
        c = tf.convert_to_tensor(c, name="c")
        # Define some computation that uses `a`, `b`, and `c`.
        return foo_op(..., name=scope)
    ```
    """
  
    @property
    def name(self):
      return self._name
  
    def __init__(self, name, default_name=None, values=None):
      """Initialize the context manager.
  
      Args:
        name: The name argument that is passed to the op function.
        default_name: The default name to use if the `name` argument is `None`.
        values: The list of `Tensor` arguments that are passed to the op function.
  
      Raises:
        TypeError: if `default_name` is passed in but not a string.
      """
      self._name_scope = name_scope(
          name, default_name, values, skip_on_eager=False)
      self._name = default_name if name is None else name
  
    def __enter__(self):
      return self._name_scope.__enter__()
  
    def __exit__(self, *exc_info):
      return self._name_scope.__exit__(*exc_info)
  
  
  def enter_eager_name_scope(ctx, name):
    """Updates the eager context to enter the given name scope."""
    old_name = ctx.scope_name
    if not name:
      scope_name = ""
    else:
      if name.endswith("/"):
        # A trailing slash breaks out of nested name scopes, indicating a
        # fully specified scope name, for compatibility with Graph.name_scope.
        scope_name = name
      else:
        scope_name = name + "/"
        if old_name:
          scope_name = old_name + scope_name
    ctx.scope_name = scope_name
    return scope_name, old_name
  
  
  @tf_export("name_scope", v1=[])
  class name_scope_v2(object):
    """A context manager for use when defining a Python op.
  
    This context manager pushes a name scope, which will make the name of all
    operations added within it have a prefix.
  
    For example, to define a new Python op called `my_op`:
  
    ```python
    def my_op(a, b, c, name=None):
      with tf.name_scope("MyOp") as scope:
        a = tf.convert_to_tensor(a, name="a")
        b = tf.convert_to_tensor(b, name="b")
        c = tf.convert_to_tensor(c, name="c")
        # Define some computation that uses `a`, `b`, and `c`.
        return foo_op(..., name=scope)
    ```
  
    When executed, the Tensors `a`, `b`, `c`, will have names `MyOp/a`, `MyOp/b`,
    and `MyOp/c`.
  
    If the scope name already exists, the name will be made unique by appending
    `_n`. For example, calling `my_op` the second time will generate `MyOp_1/a`,
    etc.
    """
  
    def __init__(self, name):
      """Initialize the context manager.
  
      Args:
        name: The prefix to use on all names created within the name scope.
  
      Raises:
        ValueError: If name is None, or not a string.
      """
      if name is None or not isinstance(name, six.string_types):
        raise ValueError("name for name_scope must be a string.")
      self._name = name
      self._exit_fns = []
  
    @property
    def name(self):
      return self._name
  
    def __enter__(self):
      """Start the scope block.
  
      Returns:
        The scope name.
  
      Raises:
        ValueError: if neither `name` nor `default_name` is provided
          but `values` are.
      """
      ctx = context.context()
      if ctx.executing_eagerly():
        scope_name, old_scope_name = enter_eager_name_scope(ctx, self._name)
        self._exit_fns.append(
            lambda *a: setattr(ctx, "scope_name", old_scope_name))
      else:
        scope = get_default_graph().name_scope(self._name)
        scope_name = scope.__enter__()
        self._exit_fns.append(scope.__exit__)
      return scope_name
  
    def __exit__(self, type_arg, value_arg, traceback_arg):
      exit_fn = self._exit_fns.pop()
      exit_fn(type_arg, value_arg, traceback_arg)
      return False  # False values do not suppress exceptions
  
  
  def strip_name_scope(name, export_scope):
    """Removes name scope from a name.
  
    Args:
      name: A `string` name.
      export_scope: Optional `string`. Name scope to remove.
  
    Returns:
      Name with name scope removed, or the original name if export_scope
      is None.
    """
    if export_scope:
      if export_scope[-1] == "/":
        export_scope = export_scope[:-1]
  
      try:
        # Strips export_scope/, export_scope///,
        # ^export_scope/, loc:@export_scope/.
        str_to_replace = r"([\^]|loc:@|^)" + export_scope + r"[\/]+(.*)"
        return re.sub(str_to_replace, r"\1\2", compat.as_str(name), count=1)
      except TypeError as e:
        # If the name is not of a type we can process, simply return it.
        logging.warning(e)
        return name
    else:
      return name
  
  
  def prepend_name_scope(name, import_scope):
    """Prepends name scope to a name.
  
    Args:
      name: A `string` name.
      import_scope: Optional `string`. Name scope to add.
  
    Returns:
      Name with name scope added, or the original name if import_scope
      is None.
    """
    if import_scope:
      if import_scope[-1] == "/":
        import_scope = import_scope[:-1]
  
      try:
        str_to_replace = r"([\^]|loc:@|^)(.*)"
        return re.sub(str_to_replace, r"\1" + import_scope + r"/\2",
                      compat.as_str(name))
      except TypeError as e:
        # If the name is not of a type we can process, simply return it.
        logging.warning(e)
        return name
    else:
      return name
  
  
  # pylint: disable=g-doc-return-or-yield
  # pylint: disable=not-context-manager
  @tf_export(v1=["op_scope"])
  @tf_contextlib.contextmanager
  def op_scope(values, name, default_name=None):
    """DEPRECATED. Same as name_scope above, just different argument order."""
    logging.warn("tf.op_scope(values, name, default_name) is deprecated,"
                 " use tf.name_scope(name, default_name, values)")
    with name_scope(name, default_name=default_name, values=values) as scope:
      yield scope
  
  
  _proto_function_registry = registry.Registry("proto functions")
  
  
  def register_proto_function(collection_name,
                              proto_type=None,
                              to_proto=None,
                              from_proto=None):
    """Registers `to_proto` and `from_proto` functions for collection_name.
  
    `to_proto` function converts a Python object to the corresponding protocol
    buffer, and returns the protocol buffer.
  
    `from_proto` function converts protocol buffer into a Python object, and
    returns the object..
  
    Args:
      collection_name: Name of the collection.
      proto_type: Protobuf type, such as `saver_pb2.SaverDef`,
        `variable_pb2.VariableDef`, `queue_runner_pb2.QueueRunnerDef`..
      to_proto: Function that implements Python object to protobuf conversion.
      from_proto: Function that implements protobuf to Python object conversion.
    """
    if to_proto and not callable(to_proto):
      raise TypeError("to_proto must be callable.")
    if from_proto and not callable(from_proto):
      raise TypeError("from_proto must be callable.")
  
    _proto_function_registry.register((proto_type, to_proto, from_proto),
                                      collection_name)
  
  
  def get_collection_proto_type(collection_name):
    """Returns the proto_type for collection_name."""
    try:
      return _proto_function_registry.lookup(collection_name)[0]
    except LookupError:
      return None
  
  
  def get_to_proto_function(collection_name):
    """Returns the to_proto function for collection_name."""
    try:
      return _proto_function_registry.lookup(collection_name)[1]
    except LookupError:
      return None
  
  
  def get_from_proto_function(collection_name):
    """Returns the from_proto function for collection_name."""
    try:
      return _proto_function_registry.lookup(collection_name)[2]
    except LookupError:
      return None
  
  
  def _operation_conversion_error(op, dtype=None, name=None, as_ref=False):
    """Produce a nice error if someone converts an Operation to a Tensor."""
    raise TypeError(("Can't convert Operation '%s' to Tensor "
                     "(target dtype=%r, name=%r, as_ref=%r)") %
                    (op.name, dtype, name, as_ref))
  
  
  def _op_to_colocate_with(v, graph):
    """Operation object corresponding to v to use for colocation constraints."""
    if v is None:
      return None
    if isinstance(v, Operation):
      return v
    # We always want to colocate with the reference op.
    # When 'v' is a ResourceVariable, the reference op is the handle creating op.
    #
    # What this should be is:
    # if isinstance(v, ResourceVariable):
    #   return v.handle.op
    # However, that would require a circular import dependency.
    # As of October 2018, there were attempts underway to remove
    # colocation constraints altogether. Assuming that will
    # happen soon, perhaps this hack to work around the circular
    # import dependency is acceptable.
    if hasattr(v, "handle") and isinstance(v.handle, Tensor):
      if graph.building_function:
        return graph.capture(v.handle).op
      else:
        return v.handle.op
    return internal_convert_to_tensor_or_indexed_slices(v, as_ref=True).op
  
  
  def _is_keras_symbolic_tensor(x):
    return hasattr(x, "graph") and getattr(x.graph, "name", None) == "keras_graph"
  
  
  tensor_conversion_registry.register_tensor_conversion_function(
      Operation, _operation_conversion_error)
  
  
  # These symbols were originally defined in this module; import them for
  # backwards compatibility until all references have been updated to access
  # them from the indexed_slices.py module.
  IndexedSlices = indexed_slices.IndexedSlices
  IndexedSlicesValue = indexed_slices.IndexedSlicesValue
  convert_to_tensor_or_indexed_slices = \
      indexed_slices.convert_to_tensor_or_indexed_slices
  convert_n_to_tensor_or_indexed_slices = \
      indexed_slices.convert_n_to_tensor_or_indexed_slices
  internal_convert_to_tensor_or_indexed_slices = \
      indexed_slices.internal_convert_to_tensor_or_indexed_slices
  internal_convert_n_to_tensor_or_indexed_slices = \
      indexed_slices.internal_convert_n_to_tensor_or_indexed_slices
  register_tensor_conversion_function = \
      tensor_conversion_registry.register_tensor_conversion_function
  
  
  # Helper functions for op wrapper modules generated by `python_op_gen`.
  
  
  def to_raw_op(f):
    """Make a given op wrapper function `f` raw.
  
    Raw op wrappers can only be called with keyword arguments.
  
    Args:
      f: An op wrapper function to make raw.
  
    Returns:
      Raw `f`.
    """
    # Copy `f` to get a new `__dict__`, otherwise `tf_export` will fail
    # due to double-registration.
    f = types.FunctionType(f.__code__, f.__globals__, f.__name__, f.__defaults__,
                           f.__closure__)
    return kwarg_only(f)
  
  
  def raise_from_not_ok_status(e, name):
    message = e.message + (" name: " + name if name is not None else "")
    # pylint: disable=protected-access
    six.raise_from(core._status_to_exception(e.code, message), None)
    # pylint: enable=protected-access
  
  
  def add_exit_callback_to_default_func_graph(fn):
    """Add a callback to run when the default function graph goes out of scope.
  
    Usage:
  
    ```python
    @tf.function
    def fn(x, v):
      expensive = expensive_object(v)
      add_exit_callback_to_default_func_graph(lambda: expensive.release())
      return g(x, expensive)
  
    fn(x=tf.constant(...), v=...)
    # `expensive` has been released.
    ```
  
    Args:
      fn: A callable that takes no arguments and whose output is ignored.
        To be executed when exiting func graph scope.
  
    Raises:
      RuntimeError: If executed when the current default graph is not a FuncGraph,
        or not currently executing in function creation mode (e.g., if inside
        an init_scope).
    """
    default_graph = get_default_graph()
    if not default_graph._building_function:  # pylint: disable=protected-access
      raise RuntimeError(
          "Cannot add scope exit callbacks when not building a function.  "
          "Default graph: {}".format(default_graph))
    default_graph._add_scope_exit_callback(fn)  # pylint: disable=protected-access
  
  
  def _reconstruct_sequence_inputs(op_def, inputs, attrs):
    """Regroups a flat list of input tensors into scalar and sequence inputs.
  
    Args:
      op_def: The `op_def_pb2.OpDef` (for knowing the input types)
      inputs: a list of input `Tensor`s to the op.
      attrs: mapping from attr name to `attr_value_pb2.AttrValue` (these define
        how long each sequence is)
  
    Returns:
      A list of `Tensor`s (corresponding to scalar inputs) and lists of
      `Tensor`s (corresponding to sequence inputs).
    """
    grouped_inputs = []
    i = 0
    for input_arg in op_def.input_arg:
      if input_arg.number_attr:
        input_len = attrs[input_arg.number_attr].i
        is_sequence = True
      elif input_arg.type_list_attr:
        input_len = len(attrs[input_arg.type_list_attr].list.type)
        is_sequence = True
      else:
        input_len = 1
        is_sequence = False
  
      if is_sequence:
        grouped_inputs.append(inputs[i:i + input_len])
      else:
        grouped_inputs.append(inputs[i])
      i += input_len
  
    assert i == len(inputs)
    return grouped_inputs
  
  
  class _TensorIterator(object):
    """Iterates over the leading dim of a Tensor. Performs no error checks."""
  
    def __init__(self, tensor, dim0):
      self._tensor = tensor
      self._index = 0
      self._limit = dim0
  
    def __iter__(self):
      return self
  
    def __next__(self):
      if self._index == self._limit:
        raise StopIteration
      result = self._tensor[self._index]
      self._index += 1
      return result
  
    next = __next__  # python2.x compatibility.
  
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