text: # 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.
  # ==============================================================================
  """Traversing Python modules and classes."""
  
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  import sys
  
  from tensorflow.python.util import tf_inspect
  
  __all__ = ['traverse']
  
  
  def _traverse_internal(root, visit, stack, path):
    """Internal helper for traverse."""
  
    # Only traverse modules and classes
    if not tf_inspect.isclass(root) and not tf_inspect.ismodule(root):
      return
  
    try:
      children = tf_inspect.getmembers(root)
    except ImportError:
      # On some Python installations, some modules do not support enumerating
      # members (six in particular), leading to import errors.
      children = []
  
    new_stack = stack + [root]
    visit(path, root, children)
    for name, child in children:
      # Do not descend into built-in modules
      if tf_inspect.ismodule(
          child) and child.__name__ in sys.builtin_module_names:
        continue
  
      # Break cycles
      if any(child is item for item in new_stack):  # `in`, but using `is`
        continue
  
      child_path = path + '.' + name if path else name
      _traverse_internal(child, visit, new_stack, child_path)
  
  
  def traverse(root, visit):
    """Recursively enumerate all members of `root`.
  
    Similar to the Python library function `os.path.walk`.
  
    Traverses the tree of Python objects starting with `root`, depth first.
    Parent-child relationships in the tree are defined by membership in modules or
    classes. The function `visit` is called with arguments
    `(path, parent, children)` for each module or class `parent` found in the tree
    of python objects starting with `root`. `path` is a string containing the name
    with which `parent` is reachable from the current context. For example, if
    `root` is a local class called `X` which contains a class `Y`, `visit` will be
    called with `('Y', X.Y, children)`).
  
    If `root` is not a module or class, `visit` is never called. `traverse`
    never descends into built-in modules.
  
    `children`, a list of `(name, object)` pairs are determined by
    `tf_inspect.getmembers`. To avoid visiting parts of the tree, `children` can
    be modified in place, using `del` or slice assignment.
  
    Cycles (determined by reference equality, `is`) stop the traversal. A stack of
    objects is kept to find cycles. Objects forming cycles may appear in
    `children`, but `visit` will not be called with any object as `parent` which
    is already in the stack.
  
    Traversing system modules can take a long time, it is advisable to pass a
    `visit` callable which blacklists such modules.
  
    Args:
      root: A python object with which to start the traversal.
      visit: A function taking arguments `(path, parent, children)`. Will be
        called for each object found in the traversal.
    """
    _traverse_internal(root, visit, [], '')
  