text: # Copyright 2018 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.
  # ==============================================================================
  # pylint: disable=unidiomatic-typecheck
  """Prototype decorator for defining graph functions with eager semantics."""
  
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  import functools
  import threading
  import weakref
  
  from tensorflow.python.eager import context
  from tensorflow.python.eager import function as function_lib
  from tensorflow.python.eager import lift_to_graph
  from tensorflow.python.framework import func_graph as func_graph_module
  from tensorflow.python.framework import ops
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import control_flow_ops
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import resource_variable_ops
  from tensorflow.python.platform import tf_logging as logging
  from tensorflow.python.training.tracking import base as trackable
  
  
  from tensorflow.python.util import nest
  from tensorflow.python.util import object_identity
  from tensorflow.python.util import tf_decorator
  from tensorflow.python.util.tf_export import tf_export
  
  FREQUENT_TRACING_WARNING_MAX_CALL_HISTORY = 10
  FREQUENT_TRACING_WARNING_THRESHOLD = 5
  
  
  class _CallCounter(object):
    """Class keeping track of how many recent calls triggered tracing."""
  
    def __init__(self, max_call_history):
      self._max_call_history = max_call_history
      self._calls_per_tracings = []
      self.call_count = 0
  
    def called_with_tracing(self):
      self.call_count += 1
      self._calls_per_tracings.append(1)
  
      while self._calls_per_tracings:
        if self.call_count - self._calls_per_tracings[0] > self._max_call_history:
          self.call_count -= self._calls_per_tracings.pop(0)
        else:
          break
  
    def called_without_tracing(self):
      # We don't count tracing when users load a concrete function dicretly or
      # call get_concrete_function, so the first call can be not a tracing call.
      if not self._calls_per_tracings:
        self._calls_per_tracings = [0]
      self._calls_per_tracings[-1] += 1
      self.call_count += 1
  
    def get_tracing_count(self):
      return len(self._calls_per_tracings)
  
  
  class UnliftedInitializerVariable(resource_variable_ops.UninitializedVariable):
    """Variable which does not lift its initializer out of function context.
  
    Instances of this variable, when created, build a graph which runs their
    initializer inside a tf.cond(is_initialized) block.
  
    This can only be created inside a defun called from (eventually) eager
    mode. That is, non-function-building graphs are not supported.
    """
  
    def __init__(self,
                 initial_value=None,
                 trainable=None,
                 caching_device=None,
                 name=None,
                 dtype=None,
                 constraint=None,
                 add_initializers_to=None,
                 lifted_initializer_graph=None,
                 synchronization=None,
                 aggregation=None,
                 shape=None,
                 **unused_kwargs):
      """Creates a variable.
  
      Args:
        initial_value: A `Tensor`, or Python object convertible to a `Tensor`,
          which is the initial value for the Variable. The initial value must have
          a shape specified unless `validate_shape` is set to False. Can also be a
          callable with no argument that returns the initial value when called.
          (Note that initializer functions from init_ops.py must first be bound
           to a shape before being used here.)
        trainable: If `True`, GradientTapes automatically watch uses of this
          Variable.
        caching_device: Optional device string or function describing where the
          Variable should be cached for reading.  Defaults to the Variable's
          device.  If not `None`, caches on another device.  Typical use is to
          cache on the device where the Ops using the Variable reside, to
          deduplicate copying through `Switch` and other conditional statements.
        name: Optional name for the variable. Defaults to `'Variable'` and gets
          uniquified automatically.
        dtype: If set, initial_value will be converted to the given type.
          If None, either the datatype will be kept (if initial_value is
         a Tensor) or float32 will be used (if it is a Python object convertible
         to a Tensor).
        constraint: An optional projection function to be applied to the variable
          after being updated by an `Optimizer` (e.g. used to implement norm
          constraints or value constraints for layer weights). The function must
          take as input the unprojected Tensor representing the value of the
          variable and return the Tensor for the projected value
          (which must have the same shape). Constraints are not safe to
          use when doing asynchronous distributed training.
        add_initializers_to: if not None and not in legacy graph mode, the
          initializer tensor will be added to this map in addition to adding the
          assignment to the function.
        lifted_initializer_graph: FuncGraph to try to lift initializers to.
        synchronization: Indicates when a distributed a variable will be
          aggregated. Accepted values are constants defined in the class
          `tf.VariableSynchronization`. By default the synchronization is set to
          `AUTO` and the current `DistributionStrategy` chooses
          when to synchronize.
        aggregation: Indicates how a distributed variable will be aggregated.
          Accepted values are constants defined in the class
          `tf.VariableAggregation`.
        shape: (optional) The shape of this variable. If None, the shape of
          `initial_value` will be used. When setting this argument to
          `tf.TensorShape(None)` (representing an unspecified shape), the variable
          can be assigned with values of different shapes.
  
      Raises:
        ValueError: If the initial value is not specified, or does not have a
          shape and `validate_shape` is `True`.
        RuntimeError: If called outside of a function definition.
      """
      with ops.init_scope():
        self._in_graph_mode = not context.executing_eagerly()
      if not ops.inside_function():
        # If we've been init_scope()d out of the function definition nothing to do
        # here; we can't really do the capturing or conditional logic.
        resource_variable_ops.ResourceVariable.__init__(
            self, initial_value=initial_value, trainable=trainable,
            caching_device=caching_device, name=name, dtype=dtype,
            constraint=constraint)
        return
      if initial_value is None:
        raise ValueError("initial_value must be specified.")
      init_from_fn = callable(initial_value)
  
      if constraint is not None and not callable(constraint):
        raise ValueError("The `constraint` argument must be a callable.")
  
      if isinstance(initial_value, trackable.CheckpointInitialValue):
        self._maybe_initialize_trackable()
        self._update_uid = initial_value.checkpoint_position.restore_uid
        initial_value = initial_value.wrapped_value
  
      with ops.name_scope(name, "Variable", []
                          if init_from_fn else [initial_value]) as scope_name:
        with ops.name_scope("Initializer"), ops.device(None):
          initial_value = ops.convert_to_tensor(
              initial_value() if init_from_fn else initial_value,
              name="initial_value", dtype=dtype)
        assert initial_value is not None
  
        # Don't use `shape or initial_value.shape` since TensorShape has
        # overridden `__bool__`.
        if shape is None:
          shape = initial_value.shape
  
      # Use the constructor for UninitializedVariable to start. Outside the name
      # scope so we don't double up the prefix.
      super(UnliftedInitializerVariable, self).__init__(
          trainable=trainable,
          caching_device=caching_device,
          name=name,
          shape=shape,
          dtype=initial_value.dtype,
          constraint=constraint,
          synchronization=synchronization,
          aggregation=aggregation,
          extra_handle_data=initial_value,
          **unused_kwargs)
  
      with ops.name_scope(scope_name):
        if self._in_graph_mode:
          with ops.init_scope():
            outer_graph = ops.get_default_graph()
          func_graph = ops.get_default_graph()
          function_placeholders = (
              func_graph.inputs + func_graph.internal_captures)
          placeholder_ops = set(
              [tensor.op for tensor in function_placeholders])
          lifted_initializer = lift_to_graph.lift_to_graph(
              [initial_value], outer_graph,
              disallowed_placeholders=placeholder_ops)[initial_value]
          with ops.init_scope():
            self._initial_value = lifted_initializer
            with ops.name_scope("IsInitialized"):
              self._is_initialized_op = (
                  resource_variable_ops.var_is_initialized_op(self._handle))
            if initial_value is not None:
              with ops.name_scope("Assign") as n, ops.colocate_with(self._handle):
                self._initializer_op = resource_variable_ops.assign_variable_op(
                    self._handle, lifted_initializer, name=n)
        elif context.executing_eagerly():
          # In this case, both current scope and init scope are eager.
          # Assign_variable_op will be executed immediately. So we don't need to
          # add it to "add_initializers_to" to lift it out.
          with ops.name_scope("Assign") as n, ops.colocate_with(self._handle):
            resource_variable_ops.assign_variable_op(
                self._handle, initial_value, name=n)
        else:
          # Init scope is eager but current scope is graph. We will lift out this
          # variable by addint it into "add_initializers_to".
          if add_initializers_to is not None:
            add_initializers_to.append((self, initial_value))
  
          def assign_fn():
            with ops.name_scope("Assign") as n, ops.colocate_with(self._handle):
              resource_variable_ops.assign_variable_op(
                  self._handle,
                  initial_value,
                  name=n)
              # Returning values to keep tf.cond happy.
            return ops.convert_to_tensor(1)
          def not_assign_fn():
            return ops.convert_to_tensor(0)
          # Note: this cond is always guaranteed to run because we're inside a
          # defun which will insert automatic control dependencies. It will only
          # execute assign_fn if lifting failed.
          graph = ops.get_default_graph()
  
          # Capture the handle ahead of time in order to avoid querying the shape
          # of the handle which helps async execution performance
          graph.capture(self._handle, shape=())
          control_flow_ops.cond(
              resource_variable_ops.var_is_initialized_op(self._handle),
              not_assign_fn, assign_fn)
  
  
  RUN_FUNCTIONS_EAGERLY = False
  
  
  @tf_export("config.experimental_run_functions_eagerly")
  def run_functions_eagerly(run_eagerly):
    """Enables / disables eager execution of `tf.function`s.
  
    Calling `tf.config.experimental_run_functions_eagerly(True)` will make all
    invocations of `tf.function` run eagerly instead of running as a traced graph
    function.
  
    This can be useful for debugging or profiling. For example, let's say you
    implemented a simple iterative sqrt function, and you want to collect the
    intermediate values and plot the convergence.  Appending the values to a list
    in `@tf.function` normally wouldn't work since it will just record the Tensors
    being traced, not the values.  Instead, you can do the following.
  
    >>> ys = []
    >>>
    >>> @tf.function
    ... def sqrt(x):
    ...   y = x / 2
    ...   d = y
    ...   for _ in range(10):
    ...     d /= 2
    ...     if y * y < x:
    ...       y += d
    ...     else:
    ...       y -= d
    ...     ys.append(y.numpy())
    ...   return y
    >>>
    >>> tf.config.experimental_run_functions_eagerly(True)
    >>> sqrt(tf.constant(2.))
    <tf.Tensor: shape=(), dtype=float32, numpy=1.4150391>
    >>> ys
    [1.5, 1.25, 1.375, 1.4375, 1.40625, 1.421875, 1.4140625, 1.4179688, 1.4160156,
    1.4150391]
    >>> tf.config.experimental_run_functions_eagerly(False)
  
    Calling `tf.config.experimental_run_functions_eagerly(False)` will undo this
    behavior.
  
    Args:
      run_eagerly: Boolean. Whether to run functions eagerly.
    """
    global RUN_FUNCTIONS_EAGERLY
    RUN_FUNCTIONS_EAGERLY = bool(run_eagerly)
  
  
  @tf_export("config.experimental_functions_run_eagerly")
  def functions_run_eagerly():
    """Returns the value of the `experimental_run_functions_eagerly` setting."""
    return RUN_FUNCTIONS_EAGERLY
  
  
  class FunctionDeleter(object):
  
    def __init__(self, func_graph):
      self.func_graph = func_graph
  
    def __del__(self):
      try:
        func_graph_module.dismantle_func_graph(self.func_graph)
      except:  # pylint: disable=bare-except
        # Note: bare except here because this can be noisy at shutdown time.
        pass
  
  
  class Function(object):
    """Wrapper class for the graph functions defined for a Python function.
  
    See the documentation for `tf.function` for more information on the semantics
    of defined functions.
  
    `Function` is thread-compatible.
    """
  
    def __init__(self,
                 python_function,
                 name,
                 input_signature=None,
                 autograph=True,
                 experimental_implements=None,
                 experimental_autograph_options=None,
                 experimental_relax_shapes=False,
                 experimental_compile=None):
      """Initializes a `Function`.
  
      Args:
        python_function: the function to be wrapped.
        name: the name given to it.
        input_signature: a possibly nested sequence of `TensorSpec` objects
          specifying the input signature of this function. If `None`, a separate
          function is instantiated for each inferred input signature.
        autograph: whether `python_function` should be converted to graph mode.
          See https://www.tensorflow.org/guide/autograph for more information.
        experimental_implements: If provided, contains a name of a "known"
          function this implements. For example "mycompany.my_recurrent_cell".
          This is stored as an attribute in the serialized representation,
          which can then be detected and manipulated when processing serialized
          graph.
          See
          https://github.com/tensorflow/community/blob/master/rfcs/20190610-standardizing-composite_ops.md
          for details.  For an example of utilizing this attribute see:
          https://github.com/tensorflow/tensorflow/blob/master/tensorflow/compiler/mlir/lite/transforms/prepare_composite_functions_tf.cc
          The code above automatically detects and substitutes function that
          implements "embedded_matmul" and allows TFLite to substitute its own
          implementations. For instance, a tensorflow user can use this
           attribute to mark that their function also implements
          `embedded_matmul``` (perhaps more efficiently!)
          by specifying it using this flag.
  
          ```python
          @tf.function(
              experimental_implements="lingvo.SimpleEmbeddingLayer.EmbMatmul")
          def embedding_matmul(a, b):
             # custom implementation here
          ```
  
        experimental_autograph_options: optional tuple of
          tensorflow.autograph.Feature values. Allows enabling additional
          conversion options when autograph is set to True.
        experimental_relax_shapes: When true, argument shapes may be relaxed to
          avoid unecessary retracing.
        experimental_compile: If false, execute the function in a regular way. The
          function is optimized by some graph rewrite passes (some ops might be
          clustered into a single op) and interpreted by the standard TensorFlow
          executor, which dispatches op kernels one by one as they become
          executable. Set it to false when directly running a multi-device
          function on TPUs (e.g. two TPU cores, one TPU core and its
          host CPU). If True, the function is compiled directly by XLA. XLA would
          fuse all the ops and emit more efficient code to run for some devices
          (e.g. TPU, XLA_GPU) and some use cases (e.g. dense tensor computation).
          It requires that the whole function is compilable by XLA. If None
          (default), compile the function with XLA when running on TPU and go
          through the regular function execution path when running on other
          devices.
  
      Raises:
        ValueError: if `input_signature` is not None and the `python_function`'s
          argspec has keyword arguments.
      """
      self._lock = threading.Lock()
      self._python_function = python_function
      self._function_spec = function_lib.FunctionSpec.from_function_and_signature(
          python_function, input_signature)
      self._implements = experimental_implements
      self._autograph = autograph
      self._experimental_autograph_options = experimental_autograph_options
      self.experimental_relax_shapes = experimental_relax_shapes
      self._experimental_compile = experimental_compile
      self._created_variables = None  # GUARDED_BY(self._lock)
      self._stateful_fn = None  # GUARDED_BY(self._lock)
      self._stateless_fn = None  # GUARDED_BY(self._lock)
      self._descriptor_cache = weakref.WeakKeyDictionary()
      self._name = name
      self._input_signature = input_signature
      self._call_counter = _CallCounter(FREQUENT_TRACING_WARNING_MAX_CALL_HISTORY)
  
    def _defun_with_scope(self, scope):
      """Creates a defun wrapped inside a variable creator scope."""
  
      weak_wrapped_fn = None
      def wrapped_fn(*args, **kwds):
        """Wraps `self._python_function` in a variable creator scope."""
        # We register a variable creator with reduced priority. If an outer
        # variable creator is just modifying keyword arguments to the variable
        # constructor, this will work harmoniously. Since the `scope` registered
        # here actually creates the variable, it taking priority would otherwise
        # ignore the outer creator.
        #
        # If an outer variable creator calls the variable constructor manually,
        # for example creating a MirroredVariable, then they won't call our
        # creator. This means we won't be able to trace the initialization graph,
        # and so variable initializers can't depend on function arguments. This is
        # better than the alternative, tracing the initialization graph but giving
        # the user a variable type they didn't want.
        with ops.get_default_graph()._variable_creator_scope(scope, priority=50):  # pylint: disable=protected-access
          # __wrapped__ allows AutoGraph to swap in a converted function. We give
          # the function a weak reference to itself to avoid a reference cycle.
          return weak_wrapped_fn().__wrapped__(*args, **kwds)
      weak_wrapped_fn = weakref.ref(wrapped_fn)
  
      return self._defun(tf_decorator.make_decorator(
          self._python_function,
          wrapped_fn))
  
    def _defun(self, fn):
      """Returns a defun generated from the input function."""
      attributes = {}
      if self._implements is not None:
        attributes[function_lib.IMPLEMENTS_ATTRIBUTE_NAME] = self._implements
      if self._experimental_compile is not None:
        attributes.update(_XlaCompile=bool(self._experimental_compile))
      if not attributes:
        attributes = None
      return function_lib.defun_with_attributes(
          fn,
          input_signature=self.input_signature,
          attributes=attributes,
          autograph=self._autograph,
          experimental_autograph_options=self._experimental_autograph_options,
          experimental_relax_shapes=self.experimental_relax_shapes)
  
    def _initialize(self, args, kwds, add_initializers_to=None):
      """Initializes, on the first call.
  
      Creates two `Function`s, one that will allow creation of variables
      and one that won't.
  
      Additionally runs a trace for the `Function` that allows creation
      of variables.
  
      Args:
        args: Arguments to the underlying python callable.
        kwds: Keyword arguments to the python callable.
        add_initializers_to: Where to collect variable initializers, if not None.
      """
  
      created_variables = []
      lifted_initializer_graph = func_graph_module.FuncGraph("initializer")
  
      def variable_capturing_scope(unused_next_creator, **kwds):
        """Creates UnliftedInitializerVariables and saves references to them."""
        v = UnliftedInitializerVariable(
            add_initializers_to=add_initializers_to,
            lifted_initializer_graph=lifted_initializer_graph, **kwds)
        created_variables.append(weakref.ref(v))
        return v
  
      self._created_variables = created_variables
      self._stateful_fn = self._defun_with_scope(variable_capturing_scope)
      self._stateful_fn._name = self._name  # pylint: disable=protected-access
      # Force the definition of the function for these arguments
      self._lifted_initializer_graph = lifted_initializer_graph
      self._graph_deleter = FunctionDeleter(self._lifted_initializer_graph)
      self._concrete_stateful_fn = (
          self._stateful_fn._get_concrete_function_internal_garbage_collected(  # pylint: disable=protected-access
              *args, **kwds))
  
      def invalid_creator_scope(*unused_args, **unused_kwds):
        """Disables variable creation."""
        raise ValueError(
            "tf.function-decorated function tried to create "
            "variables on non-first call.")
  
      self._stateless_fn = self._defun_with_scope(invalid_creator_scope)
      self._stateless_fn._name = self._name  # pylint: disable=protected-access
  
    def _clone(self, python_function):
      return Function(
          python_function=(self._python_function
                           if python_function is None else python_function),
          name=self._name,
          input_signature=self._input_signature,
          autograph=self._autograph,
          experimental_implements=self._implements,
          experimental_autograph_options=self._experimental_autograph_options,
          experimental_relax_shapes=self.experimental_relax_shapes,
          experimental_compile=self._experimental_compile)
  
    def _decorate(self, decorator):
      """Allows the captured Python function to be decorated in place.
  
      This method is only safe to call when the Function has not been called by a
      user. It makes sense to use this method to push a decorator into the
      function rather than wrapping the function in the decorator.
  
      We use this in tf.Module to allow user annotated `tf.functions` to remain as
      `Function` objects but still automatically enter the Module name_scope
      when they are evaluated like all other methods.
  
      Args:
        decorator: A callable accepting a single argument which is the function
          to decorate and returning a callable result.
  
      Raises:
        ValueError: If the function has been called a ValueError is raised.
      """
      if self._stateful_fn is not None or self._stateless_fn is not None:
        raise ValueError(
            "Functions cannot be decorated after they have been traced.")
  
      self._python_function = decorator(self._python_function)
      self._function_spec = function_lib.FunctionSpec.from_function_and_signature(
          self._python_function, self.input_signature)
  
    def _get_tracing_count(self):
      result = self._stateless_fn.tracing_count if self._stateless_fn else 0
      result += self._stateful_fn.tracing_count if self._stateful_fn else 0
      return result
  
    def __call__(self, *args, **kwds):
      """Calls the graph function and warn too frequent tracings."""
      context.ensure_initialized()
      if RUN_FUNCTIONS_EAGERLY:
        return self._python_function(*args, **kwds)
  
      tracing_count = self._get_tracing_count()
      if self._experimental_compile:
        # V2 control flow relies on XLAControlFlowContext to generate a
        # XLA-compatible function graph.
        xla_context = control_flow_ops.XLAControlFlowContext()
        try:
          xla_context.Enter()
          result = self._call(*args, **kwds)
        finally:
          xla_context.Exit()
      else:
        result = self._call(*args, **kwds)
  
      if tracing_count == self._get_tracing_count():
        self._call_counter.called_without_tracing()
        return result
  
      self._call_counter.called_with_tracing()
      recent_tracing_count = self._call_counter.get_tracing_count()
      if recent_tracing_count >= FREQUENT_TRACING_WARNING_THRESHOLD:
        logging.warning(
            "{} out of the last {} calls to {} triggered tf.function retracing. "
            "Tracing is expensive and the excessive number of tracings is likely "
            "due to passing python objects instead of tensors. Also, tf.function "
            "has experimental_relax_shapes=True option that relaxes argument "
            "shapes that can avoid unnecessary retracing. Please refer to "
            "https://www.tensorflow.org/tutorials/customization/performance#python_or_tensor_args"
            " and https://www.tensorflow.org/api_docs/python/tf/function for more "
            "details.".format(recent_tracing_count, self._call_counter.call_count,
                              self._python_function))
  
      return result
  
    def _call(self, *args, **kwds):
      """Calls the graph function."""
      self._lock.acquire()
      if self._created_variables:
        # Release the lock early so that multiple threads can perform the call
        # in parallel.
        self._lock.release()
        # In this case we have created variables on the first call, so we run the
        # defunned version which is guaranteed to never create variables.
        return self._stateless_fn(*args, **kwds)  # pylint: disable=not-callable
      elif self._stateful_fn is not None:
        # Release the lock early so that multiple threads can perform the call
        # in parallel.
        self._lock.release()
        # In this case we have not created variables on the first call. So we can
        # run the first trace but we should fail if variables are created.
        results = self._stateful_fn(*args, **kwds)
        if self._created_variables:
          raise ValueError("Creating variables on a non-first call to a function"
                           " decorated with tf.function.")
        return results
  
      try:
        # This is the first call of __call__, so we have to initialize.
        initializers = []
        self._initialize(args, kwds, add_initializers_to=initializers)
      finally:
        # At this point we know that the initialization is complete (or less
        # interestingly an exception was raised) so we no longer need a lock.
        self._lock.release()
  
      if self._created_variables:
        try:
          # Attempt to initialize variables eagerly and without conds by lifting
          # out initialization graphs. This is the only initialization strategy
          # compatible with XLA at the moment.
          self._initialize_uninitialized_variables(initializers)
        except lift_to_graph.UnliftableError:
          pass  # Fall through to cond-based initialization.
        else:
          # Lifting succeeded, so variables are initialized and we can run the
          # stateless function.
          return self._stateless_fn(*args, **kwds)
      else:
        canon_args, canon_kwds = \
            self._stateful_fn._function_spec.canonicalize_function_inputs(  # pylint: disable=protected-access
                *args, **kwds)
        # If we did not create any variables the trace we have is good enough.
        return self._concrete_stateful_fn._filtered_call(canon_args, canon_kwds)  # pylint: disable=protected-access
  
      def fn_with_cond(*inner_args, **inner_kwds):
        """Conditionally runs initialization if it's needed."""
        condition = True
        for wr in self._created_variables:
          variable = wr()
          if variable is None:
            raise ValueError(
                "A tf.Variable created inside your tf.function has been"
                " garbage-collected. Your code needs to keep Python references"
                " to variables created inside `tf.function`s.\n"
                "\n"
                "A common way to raise this error is to create and return a"
                " variable only referenced inside your function:\n"
                "\n"
                "@tf.function\n"
                "def f():\n"
                "  v = tf.Variable(1.0)\n"
                "  return v\n"
                "\n"
                "v = f()  # Crashes with this error message!\n"
                "\n"
                "The reason this crashes is that @tf.function annotated"
                " function returns a **`tf.Tensor`** with the **value** of the"
                " variable when the function is called rather than the"
                " variable instance itself. As such there is no code holding a"
                " reference to the `v` created inside the function and Python"
                " garbage collects it.\n"
                "\n"
                "The simplest way to fix this issue is to create variables"
                " outside the function and capture them:\n"
                "\n"
                "v = tf.Variable(1.0)\n"
                "\n"
                "@tf.function\n"
                "def f():\n"
                "  return v\n"
                "\n"
                "f()  # <tf.Tensor: numpy=1.>\n"
                "v.assign_add(1.)\n"
                "f()  # <tf.Tensor: numpy=2.>")
          condition = math_ops.logical_and(
              condition, resource_variable_ops.var_is_initialized_op(
                  variable.handle))
        # We want to call stateless_fn if possible because it avoids recomputing
        # potentially expensive initializers.
        return control_flow_ops.cond(
            condition,
            lambda: self._stateless_fn(*inner_args, **inner_kwds),
            functools.partial(self._concrete_stateful_fn._filtered_call,  # pylint: disable=protected-access
                              inner_args, inner_kwds))
  
      # We've created variables and are unable to lift the initialization graphs,
      # so we fall back to initializing with conds while running the function.
      canon_args, canon_kwds = \
          self._stateful_fn._function_spec.canonicalize_function_inputs(  # pylint: disable=protected-access
              *args, **kwds)
      return function_lib.defun(fn_with_cond)(*canon_args, **canon_kwds)
  
    @property
    def python_function(self):
      """The python function wrapped in this tf.function."""
      return self._python_function
  
    @property
    def input_signature(self):
      return self._function_spec.input_signature
  
    @property
    def function_spec(self):
      return self._function_spec
  
    def _initialize_uninitialized_variables(self, initializers):
      """Make and call a `ConcreteFunction` which initializes variables."""
  
      if not initializers:
        return
  
      # Note: using defun here avoids an infinite recursion.
      @function_lib.defun
      def initialize_variables():
        op_map = object_identity.ObjectIdentityDictionary()
        # Stack all the var_is_initialized values into one tensor and intepret the
        # numpy value. This will reduce the number of RPCs between client and
        # worker in the remote case.
        with ops.init_scope():
          var_is_initialized = []
          for v, _ in initializers:
            var_is_initialized.append(
                resource_variable_ops.var_is_initialized_op(v.handle))
          var_is_initialized = array_ops.stack(var_is_initialized).numpy()
  
        inits = []
        for (v, init), is_initialized in zip(initializers, var_is_initialized):
          with ops.init_scope():
            if is_initialized:
              continue
          inits.append(init)
  
        if inits:
          op_map = lift_to_graph.lift_to_graph(
              inits, ops.get_default_graph(), op_map=op_map)
        for (v, init), is_initialized in zip(initializers, var_is_initialized):
          with ops.init_scope():
            if is_initialized:
              continue
          v.assign(op_map[init], read_value=False)
  
      with ops.init_scope():
        return initialize_variables.get_concrete_function()()
  
    def get_initialization_function(self, *args, **kwargs):
      """Returns a `ConcreteFunction` which initializes this function's variables.
  
      Requires that this function hasn't been accessed yet through either calling
      it or calling get_concrete_function. Fails if we cannot build an initializer
      function which does not depend on the concrete values of the inputs to this
      function.
  
      Note that running this function will overwrite any values currently assigned
      to variables, for example restores from a checkpoint.
  
      Args:
        *args: arguments to the underlying python callable.
        **kwargs: keyword arguments to the python callable.
  
      Returns:
        A `ConcreteFunction` object which initializes the variables of this
        function.
  
      Raises:
        RuntimeError: if called after the variables have been initialized.
      """
      with self._lock:
        if self._stateful_fn is not None:
          raise RuntimeError(
              "get_initialization_function cannot be called after the function "
              "has been used")
        # Here we trace the function, collect the initializers, and attempt to
        # extract them and run them eagerly. Fail only if we cannot do so.
        initializers = []
        self._initialize(args, kwargs, add_initializers_to=initializers)
  
      # Note: using defun here avoids an infinite recursion.
      @function_lib.defun
      def initialize_variables():
        for v, init in initializers:
          v.assign(
              lift_to_graph.lift_to_graph([init], ops.get_default_graph())[init],
              read_value=False)
  
      return initialize_variables.get_concrete_function()
  
    def _list_all_concrete_functions_for_serialization(self):
      """Returns all concrete functions for serialization.
  
      Returns:
        A list of instances of `Function`.
      """
      if self.input_signature is not None:
        self.get_concrete_function()
      concrete_functions = []
      # pylint: disable=protected-access
      if self._stateful_fn:
        concrete_functions.extend(
            self._stateful_fn._function_cache.all_values())
      if self._stateless_fn:
        concrete_functions.extend(
            self._stateless_fn._function_cache.all_values())
      # pylint: enable=protected-access
      seen_signatures = []
      for concrete_function in concrete_functions:
        signature = concrete_function.structured_input_signature
        flattened = nest.flatten(signature)
        if any(
            isinstance(arg, func_graph_module.UnknownArgument)
            for arg in flattened):
          logging.info("Unsupported signature for serialization: %s.", signature)
          continue
        equal_to_signature = functools.partial(
            function_lib.is_same_structure, signature, check_values=True)
        if not any(equal_to_signature(s) for s in seen_signatures):
          seen_signatures.append(signature)
  
      # Re-create concrete functions for these signatures. Re-creating ensures
      # that if the cache key has changed, the function will be traced again.
      concrete_functions = []
      for args, kwargs in seen_signatures:
        concrete_functions.append(self.get_concrete_function(*args, **kwargs))
      return concrete_functions
  
    def _get_concrete_function_garbage_collected(self, *args, **kwargs):
      """Returns a `ConcreteFunction` specialized to inputs and execution context.
  
      Unlike `get_concrete_function(...)`, the graph will be deleted when the
      returned function is deleted.  It's useful to avoid creating a reference
      cycle when you know for sure that the graph will be no longer used without
      the returned function.
  
      Args:
        *args: inputs to specialize on.
        **kwargs: inputs to specialize on.
  
      Returns:
        A TensorFlow function which takes exactly one `tf.Tensor` per argument.
  
      Raises:
        ValueError: if this object has not yet been called on concrete values.
      """
      with self._lock:
        if self._stateful_fn is None:
          initializers = []
          self._initialize(args, kwargs, add_initializers_to=initializers)
          self._initialize_uninitialized_variables(initializers)
  
      if self._created_variables:
        # In this case we have created variables on the first call, so we run the
        # defunned version which is guaranteed to never create variables.
        return self._stateless_fn._get_concrete_function_garbage_collected(  # pylint: disable=protected-access
            *args, **kwargs)
      elif self._stateful_fn is not None:
        # In this case we have not created variables on the first call. So we can
        # run the first trace but we should fail if variables are created.
        concrete = self._stateful_fn._get_concrete_function_garbage_collected(  # pylint: disable=protected-access
            *args, **kwargs)
        if self._created_variables:
          raise ValueError("Creating variables on a non-first call to a function"
                           " decorated with tf.function.")
        return concrete
  
    def get_concrete_function(self, *args, **kwargs):
      """Returns a `ConcreteFunction` specialized to inputs and execution context.
  
      If this `Function` was created with an `input_signature`, `args` and
      `kwargs` may be omitted. With an input signature there is only one
      concrete function associated with this `Function`.
  
      If there is no fixed `input_signature` associated with this
      `Function`, positional and keyword arguments to `get_concrete_function`
      follow the same rules as input signature specification, with `tf.TensorSpec`
      objects describing `tf.Tensor`s which will be passed to the concrete
      function.
  
      Each `tf.Tensor` argument to the concrete function must have a unique name,
      either because it is the only one associated with a named argument of the
      Python function or because an explicit `name=` was passed to its
      `tf.TensorSpec` object. These names become the argument names for the
      concrete function.
  
      Arguments to the concrete function may always be specified as keyword
      arguments, naming the Tensor input. Positional arguments may be used instead
      when each preceding argument to the Python function is a Tensor.
  
      ```python
      @tf.function
      def f(x):
        return x
  
      f_concrete = f.get_concrete_function(tf.TensorSpec([], tf.float64))
      f_concrete(tf.constant(1.))
      f_concrete(x=tf.constant(1.))
      ```
  
      Nested structures containing Tensors may be specified when retrieving
      concrete functions. Structures with multiple Tensors are expanded into
      multiple arguments of the concrete function. Since multiple concrete
      function arguments are associated with one argument to the original
      function, these Tensors must be named explicitly. Tensors in nested
      structures may not be passed using positional arguments when calling the
      concrete function.
  
      ```python
      f_concrete2 = f.get_concrete_function(
          (tf.TensorSpec(None, tf.float64, name="first"),
           tf.TensorSpec([], tf.float32, name="second")))
      # Keyword arguments are required when identifying Tensors in nested
      # structures.
      f_concrete2(first=tf.constant([1.]), second=tf.constant(0.))
      ```
  
      Functions with fixed input signatures have only one concrete function
      associated with them, which can be retrieved without specifying any
      arguments. As before Tensors must have unique names, either inferred from
      the argument names in the original Python function or specified
      explicitly.
  
      ```python
      @tf.function(input_signature=(tf.TensorSpec(None, tf.float32)))
      def f_sig(y):
        return y
  
      f_sig_concrete = f.get_concrete_function()
      f_sig_concrete(tf.constant(1.))
      f_sig_concrete(y=tf.constant(1.))
      ```
  
      Args:
        *args: inputs to specialize on.
        **kwargs: inputs to specialize on.
  
      Returns:
        A TensorFlow function which takes exactly one `tf.Tensor` per argument.
  
      Raises:
        ValueError: if this object has not yet been called on concrete values.
      """
      concrete = self._get_concrete_function_garbage_collected(*args, **kwargs)
      concrete._garbage_collector.release()  # pylint: disable=protected-access
      return concrete
  
    def __get__(self, instance, owner):
      """Makes it possible to defun instance methods."""
      del owner
      # `instance` here is the instance that this `Function` was accessed through
      # e.g., for
      #
      #   class Foo(object):
      #
      #     @function.defun
      #     def bar(self):
      #       ...
      #
      #   foo = Foo()
      #   foo.bar()  # `foo.bar` is a `Function` instance
      #
      # then `instance` will be `foo` (and `owner` will be `Foo`).  We create a
      # new instance of `Function` here to allow different instances each
      # to create variables once, thereby allowing methods to be decorated with
      # tf.function. Keeps a cache to avoid retracing the function every time the
      # descriptor is accessed.
      if instance not in self._descriptor_cache:
        if instance is None:
          return self
        self._descriptor_cache[instance] = (
            function_lib.class_method_to_instance_method(self, instance))
      return self._descriptor_cache[instance]
  
  
  @tf_export("function")
  def function(func=None,
               input_signature=None,
               autograph=True,
               experimental_implements=None,
               experimental_autograph_options=None,
               experimental_relax_shapes=False,
               experimental_compile=None):
    """Compiles a function into a callable TensorFlow graph.
  
    `tf.function` constructs a callable that executes a TensorFlow graph
    (`tf.Graph`) created by trace-compiling the TensorFlow operations in `func`,
    effectively executing `func` as a TensorFlow graph.
  
    Example usage:
  
    >>> @tf.function
    ... def f(x, y):
    ...   return x ** 2 + y
    >>> x = tf.constant([2, 3])
    >>> y = tf.constant([3, -2])
    >>> f(x, y)
    <tf.Tensor: ... numpy=array([7, 7], ...)>
  
    _Features_
  
    `func` may use data-dependent control flow, including `if`, `for`, `while`
    `break`, `continue` and `return` statements:
  
    >>> @tf.function
    ... def f(x):
    ...   if tf.reduce_sum(x) > 0:
    ...     return x * x
    ...   else:
    ...     return -x // 2
    >>> f(tf.constant(-2))
    <tf.Tensor: ... numpy=1>
  
    `func`'s closure may include `tf.Tensor` and `tf.Variable` objects:
  
    >>> @tf.function
    ... def f():
    ...   return x ** 2 + y
    >>> x = tf.constant([-2, -3])
    >>> y = tf.Variable([3, -2])
    >>> f()
    <tf.Tensor: ... numpy=array([7, 7], ...)>
  
    `func` may also use ops with side effects, such as `tf.print`, `tf.Variable`
    and others:
  
    >>> v = tf.Variable(1)
    >>> @tf.function
    ... def f(x):
    ...   for i in tf.range(x):
    ...     v.assign_add(i)
    >>> f(3)
    >>> v
    <tf.Variable ... numpy=4>
  
    Important: Any Python side-effects (appending to a list, printing with
    `print`, etc) will only happen once, when `func` is traced. To have
    side-effects executed into your `tf.function` they need to be written
    as TF ops:
  
    >>> l = []
    >>> @tf.function
    ... def f(x):
    ...   for i in x:
    ...     l.append(i + 1)    # Caution! Will only happen once when tracing
    >>> f(tf.constant([1, 2, 3]))
    >>> l
    [<tf.Tensor ...>]
  
    Instead, use TensorFlow collections like `tf.TensorArray`:
  
    >>> @tf.function
    ... def f(x):
    ...   ta = tf.TensorArray(dtype=tf.int32, size=0, dynamic_size=True)
    ...   for i in range(len(x)):
    ...     ta = ta.write(i, x[i] + 1)
    ...   return ta.stack()
    >>> f(tf.constant([1, 2, 3]))
    <tf.Tensor: ..., numpy=array([2, 3, 4], ...)>
  
    _`tf.function` is polymorphic_
  
    Internally, `tf.function` can build more than one graph, to support arguments
    with different data types or shapes, since TensorFlow can build more
    efficient graphs that are specialized on shapes and dtypes. `tf.function`
    also treats any pure Python value as opaque objects, and builds a separate
    graph for each set of Python arguments that it encounters.
  
    To obtain an individual graph, use the `get_concrete_function` method of
    the callable created by `tf.function`. It can be called with the same
    arguments as `func` and returns a special `tf.Graph` object:
  
    >>> @tf.function
    ... def f(x):
    ...   return x + 1
    >>> isinstance(f.get_concrete_function(1).graph, tf.Graph)
    True
  
    Caution: Passing python scalars or lists as arguments to `tf.function` will
    always build a new graph. To avoid this, pass numeric arguments as Tensors
    whenever possible:
  
    >>> @tf.function
    ... def f(x):
    ...   return tf.abs(x)
    >>> f1 = f.get_concrete_function(1)
    >>> f2 = f.get_concrete_function(2)  # Slow - builds new graph
    >>> f1 is f2
    False
    >>> f1 = f.get_concrete_function(tf.constant(1))
    >>> f2 = f.get_concrete_function(tf.constant(2))  # Fast - reuses f1
    >>> f1 is f2
    True
  
    Python numerical arguments should only be used when they take few distinct
    values, such as hyperparameters like the number of layers in a neural network.
  
    _Input signatures_
  
    For Tensor arguments, `tf.function` instantiates a separate graph for every
    unique set of input shapes and datatypes. The example below creates two
    separate graphs, each specialized to a different shape:
  
    >>> @tf.function
    ... def f(x):
    ...   return x + 1
    >>> vector = tf.constant([1.0, 1.0])
    >>> matrix = tf.constant([[3.0]])
    >>> f.get_concrete_function(vector) is f.get_concrete_function(matrix)
    False
  
    An "input signature" can be optionally provided to `tf.function` to control
    the graphs traced. The input signature specifies the shape and type of each
    Tensor argument to the function using a `tf.TensorSpec` object. More general
    shapes can be used. This is useful to avoid creating multiple graphs when
    Tensors have dynamic shapes. It also restricts the dhape and datatype of
    Tensors that can be used:
  
    >>> @tf.function(
    ...     input_signature=[tf.TensorSpec(shape=None, dtype=tf.float32)])
    ... def f(x):
    ...   return x + 1
    >>> vector = tf.constant([1.0, 1.0])
    >>> matrix = tf.constant([[3.0]])
    >>> f.get_concrete_function(vector) is f.get_concrete_function(matrix)
    True
  
    _Variables may only be created once_
  
    `tf.function` only allows creating new `tf.Variable` objects when it is called
    for the first time:
  
    >>> class MyModule(tf.Module):
    ...   def __init__(self):
    ...     self.v = None
    ...
    ...   @tf.function
    ...   def call(self, x):
    ...     if self.v is None:
    ...       self.v = tf.Variable(tf.ones_like(x))
    ...     return self.v * x
  
    In general, it is recommended to create stateful objects like `tf.Variable`
    outside of `tf.function` and passing them as arguments.
  
    Args:
      func: the function to be compiled. If `func` is None, `tf.function` returns
        a decorator that can be invoked with a single argument - `func`. In other
        words, `tf.function(input_signature=...)(func)` is equivalent to
        `tf.function(func, input_signature=...)`. The former can be used as
        decorator.
      input_signature: A possibly nested sequence of `tf.TensorSpec` objects
        specifying the shapes and dtypes of the Tensors that will be supplied to
        this function. If `None`, a separate function is instantiated for each
        inferred input signature.  If input_signature is specified, every input to
        `func` must be a `Tensor`, and `func` cannot accept `**kwargs`.
      autograph: Whether autograph should be applied on `func` before tracing a
        graph. Data-dependent control flow requires `autograph=True`. For more
        information, see the [tf.function and AutoGraph guide](
        https://www.tensorflow.org/guide/function).
      experimental_implements: If provided, contains a name of a "known" function
        this implements. For example "mycompany.my_recurrent_cell".
        This is stored as an attribute in inference function,
        which can then be detected when processing serialized function.
        See
        https://github.com/tensorflow/community/blob/master/rfcs/20190610-standardizing-composite_ops.md
        for details.  For an example of utilizing this attribute see:
        https://github.com/tensorflow/tensorflow/blob/master/tensorflow/compiler/mlir/lite/transforms/prepare_composite_functions_tf.cc
        The code above automatically detects and substitutes function that
        implements "embedded_matmul" and allows TFLite to substitute its own
        implementations. For instance, a tensorflow user can use this
         attribute to mark that their function also implements
        `embedded_matmul``` (perhaps more efficiently!)
        by specifying it using this flag.
  
          ```python
          @tf.function(experimental_implements="embedded_matmul"):
          def embedding_matmul(a, b):
             # custom implementation here
          ```
  
      experimental_autograph_options: Optional tuple of
        `tf.autograph.experimental.Feature` values.
      experimental_relax_shapes: When True, `tf.function` may generate fewer,
        graphs that are less specialized on input shapes.
      experimental_compile: If True, the function is always compiled by
        [XLA](https://www.tensorflow.org/xla). XLA may be more efficient in some
        cases (e.g. TPU, XLA_GPU, dense tensor computations).
  
    Returns:
       If `func` is not None, returns a callable that will execute the compiled
       function (and return zero or more `tf.Tensor` objects).
       If `func` is None, returns a decorator that, when invoked with a single
       `func` argument, returns a callable equivalent to the case above.
    """
    if input_signature is not None:
      function_lib.validate_signature(input_signature)
  
    def decorated(inner_function):
      try:
        name = inner_function.__name__
      except AttributeError:
        name = "function"
      return tf_decorator.make_decorator(
          inner_function,
          Function(
              inner_function,
              name,
              input_signature=input_signature,
              autograph=autograph,
              experimental_autograph_options=experimental_autograph_options,
              experimental_relax_shapes=experimental_relax_shapes,
              experimental_compile=experimental_compile,
              experimental_implements=experimental_implements))
  
    # This code path is for the `foo = tf.function(foo, ...)` use case
    if func is not None:
      return decorated(func)
  
    # This code path is for the
    #
    # @tf.function(...)
    # def foo(...):
    #    ...
    #
    # use case, which is equivalent to `foo = tf.function(...)(foo)`
    return decorated
  