xref: /external/tensorflow/tensorflow/python/ops/resource_variable_ops.py

# Copyright 2016 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.
# ==============================================================================
"""Ops to use variables as resources."""

# pylint: disable=g-bad-name
from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

import contextlib
import functools
import weakref

import numpy as np

from tensorflow.core.framework import attr_value_pb2
from tensorflow.core.framework import variable_pb2
from tensorflow.python.client import pywrap_tf_session
from tensorflow.python.eager import context
from tensorflow.python.eager import tape
from tensorflow.python.framework import auto_control_deps_utils as acd
from tensorflow.python.framework import constant_op
from tensorflow.python.framework import cpp_shape_inference_pb2
from tensorflow.python.framework import dtypes
from tensorflow.python.framework import errors
from tensorflow.python.framework import ops
from tensorflow.python.framework import tensor_shape
from tensorflow.python.framework import tensor_spec
from tensorflow.python.ops import array_ops
from tensorflow.python.ops import gen_array_ops
from tensorflow.python.ops import gen_resource_variable_ops
from tensorflow.python.ops import gen_state_ops
from tensorflow.python.ops import handle_data_util
from tensorflow.python.ops import math_ops
from tensorflow.python.ops import state_ops
from tensorflow.python.ops import variables
# go/tf-wildcard-import
# pylint: disable=wildcard-import
from tensorflow.python.ops.gen_resource_variable_ops import *
# pylint: enable=wildcard-import
from tensorflow.python.training.tracking import base as trackable
from tensorflow.python.types import core
from tensorflow.python.util import _pywrap_utils
from tensorflow.python.util import compat
from tensorflow.python.util.deprecation import deprecated
from tensorflow.python.util.tf_export import tf_export

acd.register_read_only_resource_op("ReadVariableOp")
acd.register_read_only_resource_op("VariableShape")
acd.register_read_only_resource_op("ResourceGather")
acd.register_read_only_resource_op("ResourceGatherNd")
acd.register_read_only_resource_op("_ReadVariablesOp")


# TODO(allenl): Remove this alias and migrate callers.
get_resource_handle_data = handle_data_util.get_resource_handle_data


def get_eager_safe_handle_data(handle):
  """Get the data handle from the Tensor `handle`."""
  assert isinstance(handle, ops.Tensor)

  if isinstance(handle, ops.EagerTensor):
    return handle._handle_data  # pylint: disable=protected-access
  else:
    return get_resource_handle_data(handle)


def _set_handle_shapes_and_types(tensor, handle_data, graph_mode):
  """Sets the shape inference result HandleData on tensor.

  Args:
    tensor: A `Tensor` or `EagerTensor`.
    handle_data: A `CppShapeInferenceResult.HandleData`.
    graph_mode: A python bool.
  """
  tensor._handle_data = handle_data  # pylint: disable=protected-access
  if not graph_mode:
    return

  # Not an EagerTensor, so a graph tensor.
  shapes, types = zip(*[(pair.shape, pair.dtype)
                        for pair in handle_data.shape_and_type])
  ranks = [len(s.dim) if not s.unknown_rank else -1 for s in shapes]
  shapes = [
      [d.size for d in s.dim]  # pylint: disable=g-complex-comprehension
      if not s.unknown_rank else None for s in shapes
  ]
  pywrap_tf_session.TF_GraphSetOutputHandleShapesAndTypes_wrapper(
      tensor._op._graph._c_graph,  # pylint: disable=protected-access
      tensor._as_tf_output(),  # pylint: disable=protected-access
      shapes,
      ranks,
      types)


def _combine_handle_data(handle, initial_value):
  """Concats HandleData from tensors `handle` and `initial_value`.

  Args:
    handle: A `Tensor` of dtype `resource`.
    initial_value: A `Tensor`.

  Returns:
    A `CppShapeInferenceResult.HandleData`.  If `initial_value` has dtype
    `variant`, the `HandleData` contains the concatenation of the shape_and_type
    from both `handle` and `initial_value`.

  Raises:
    RuntimeError: If handle, which was returned by VarHandleOp, either has
      no handle data, or its len(handle_data.shape_and_type) != 1.
  """
  assert handle.dtype == dtypes.resource

  variable_handle_data = get_eager_safe_handle_data(handle)

  if initial_value.dtype != dtypes.variant:
    return variable_handle_data

  extra_handle_data = get_eager_safe_handle_data(initial_value)
  if extra_handle_data is not None and extra_handle_data.is_set:
    if (variable_handle_data is None or not variable_handle_data.is_set or
        len(variable_handle_data.shape_and_type) != 1):
      raise RuntimeError(
          "Expected VarHandleOp to return a length==1 shape_and_type, "
          "but saw: '%s'" % (variable_handle_data,))
    variable_handle_data.shape_and_type.extend(extra_handle_data.shape_and_type)
  return variable_handle_data


def _variable_handle_from_shape_and_dtype(shape,
                                          dtype,
                                          shared_name,
                                          name,
                                          graph_mode,
                                          initial_value=None):
  """Create a variable handle, copying in handle data from `initial_value`."""
  container = ops.get_default_graph()._container  # pylint: disable=protected-access
  if container is None:
    container = ""
  shape = tensor_shape.as_shape(shape)
  dtype = dtypes.as_dtype(dtype)
  if not graph_mode:
    if shared_name is not None:
      raise errors.InternalError(
          "Using an explicit shared_name is not supported executing eagerly.")
    shared_name = context.shared_name()

  handle = gen_resource_variable_ops.var_handle_op(
      shape=shape,
      dtype=dtype,
      shared_name=shared_name,
      name=name,
      container=container)
  if initial_value is None:
    initial_value = handle
  if graph_mode:
    full_handle_data = _combine_handle_data(handle, initial_value)
    _set_handle_shapes_and_types(handle, full_handle_data, graph_mode)
    return handle
  else:
    handle_data = cpp_shape_inference_pb2.CppShapeInferenceResult.HandleData()
    handle_data.is_set = True
    handle_data.shape_and_type.append(
        cpp_shape_inference_pb2.CppShapeInferenceResult.HandleShapeAndType(
            shape=shape.as_proto(), dtype=dtype.as_datatype_enum))

    if initial_value is not None and initial_value.dtype == dtypes.variant:
      extra_handle_data = get_eager_safe_handle_data(initial_value)
      if extra_handle_data is not None and extra_handle_data.is_set:
        if (not handle_data.is_set or len(handle_data.shape_and_type) != 1):
          raise RuntimeError(
              "Expected VarHandleOp to return a length==1 shape_and_type, "
              "but saw: '%s'" % (handle_data,))
        handle_data.shape_and_type.extend(extra_handle_data.shape_and_type)

    _set_handle_shapes_and_types(handle, handle_data, graph_mode)
    return handle


def eager_safe_variable_handle(initial_value, shape, shared_name, name,
                               graph_mode):
  """Creates a variable handle with information to do shape inference.

  The dtype is read from `initial_value` and stored in the returned
  resource tensor's handle data.

  If `initial_value.dtype == tf.variant`, we additionally extract the handle
  data (if any) from `initial_value` and append it to the `handle_data`.
  In this case, the returned tensor's handle data is in the form

  ```
  is_set: true
  shape_and_type {
    shape {
      // initial_value.shape
    }
    dtype: DT_VARIANT
  }
  shape_and_type {
    // handle_data(initial_value).shape_and_type[0]
  }
  shape_and_type {
    // handle_data(initial_value).shape_and_type[1]
  }
  ...
  ```

  Ops that read from this tensor, such as `ReadVariableOp` and
  `AssignVariableOp`, know that `handle_data(handle).shape_and_type[1:]`
  correspond to the handle data of the variant(s) stored in the Variable.

  Args:
    initial_value: A `Tensor`.
    shape: The shape of the handle data. Can be `TensorShape(None)` (i.e.
      unknown shape).
    shared_name: A string.
    name: A string.
    graph_mode: A python bool.

  Returns:
    The handle, a `Tensor` of type `resource`.
  """
  dtype = initial_value.dtype.base_dtype
  return _variable_handle_from_shape_and_dtype(shape, dtype, shared_name, name,
                                               graph_mode, initial_value)


@contextlib.contextmanager
def _handle_graph(handle):
  # Note: might have an eager tensor but not be executing eagerly when building
  # functions.
  if (context.executing_eagerly() or isinstance(handle, ops.EagerTensor) or
      ops.has_default_graph()):
    yield
  else:
    with handle.graph.as_default():
      yield


class EagerResourceDeleter(object):
  """An object which cleans up a resource handle.

  An alternative to defining a __del__ method on an object. The intended use is
  that ResourceVariables or other objects with resource handles will maintain a
  single reference to this object. When the parent object is collected, this
  object will be too. Even if the parent object is part of a reference cycle,
  the cycle will be collectable.
  """

  __slots__ = ["_handle", "_handle_device", "_context"]

  def __init__(self, handle, handle_device):
    if not isinstance(handle, ops.Tensor):
      raise ValueError(
          ("Passed handle=%s to EagerResourceDeleter. Was expecting a handle "
           "Tensor." % (handle,)))
    self._handle = handle
    self._handle_device = handle_device
    # This is held since the __del__ function runs an op, and if the context()
    # is collected before this object, there will be a segfault when running the
    # op.
    self._context = context.context()

  def __del__(self):
    # Resources follow object-identity when executing eagerly, so it is safe to
    # delete the resource we have a handle to.
    try:
      # A packed EagerTensor doesn't own any resource.
      if isinstance(self._handle, ops.EagerTensor) and self._handle.is_packed:
        return
      # This resource was created in eager mode. However, this destructor may be
      # running in graph mode (especially during unit tests). To clean up
      # successfully, we switch back into eager mode temporarily.
      with context.eager_mode():
        with ops.device(self._handle_device):
          gen_resource_variable_ops.destroy_resource_op(
              self._handle, ignore_lookup_error=True)
    except TypeError:
      # Suppress some exceptions, mainly for the case when we're running on
      # module deletion. Things that can go wrong include the context module
      # already being unloaded, self._handle._handle_data no longer being
      # valid, and so on. Printing warnings in these cases is silly
      # (exceptions raised from __del__ are printed as warnings to stderr).
      pass  # 'NoneType' object is not callable when the handle has been
      # partially unloaded.
    except AttributeError:
      pass  # 'NoneType' object has no attribute 'eager_mode' when context has
      # been unloaded. Will catch other module unloads as well.


def shape_safe_assign_variable_handle(handle, shape, value, name=None):
  """Helper that checks shape compatibility and assigns variable."""
  with _handle_graph(handle):
    value_tensor = ops.convert_to_tensor(value)
  shape.assert_is_compatible_with(value_tensor.shape)
  return gen_resource_variable_ops.assign_variable_op(
      handle, value_tensor, name=name)


def _maybe_set_handle_data(dtype, handle, tensor):
  if dtype == dtypes.variant:
    # For DT_VARIANT types, the handle's shape_and_type[1:] stores the
    # variant's handle data.  Extract it.
    handle_data = get_eager_safe_handle_data(handle)
    if handle_data.is_set and len(handle_data.shape_and_type) > 1:
      tensor._handle_data = (  # pylint: disable=protected-access
          cpp_shape_inference_pb2.CppShapeInferenceResult.HandleData(
              is_set=True, shape_and_type=handle_data.shape_and_type[1:]))


def variable_accessed(variable):
  """Records that `variable` was accessed for the tape and FuncGraph."""
  if hasattr(ops.get_default_graph(), "watch_variable"):
    ops.get_default_graph().watch_variable(variable)
  if variable.trainable:
    tape.variable_accessed(variable)


class BaseResourceVariable(variables.VariableV1, core.Tensor):
  """A python variable from an existing handle."""

  # TODO(wangpeng): Deprecate `constraint` when callers no long pass it in.
  def __init__(  # pylint: disable=super-init-not-called
      self,
      trainable=None,
      shape=None,
      dtype=None,
      handle=None,
      constraint=None,
      synchronization=None,
      aggregation=None,
      distribute_strategy=None,
      name=None,
      unique_id=None,
      handle_name=None,
      graph_element=None,
      initial_value=None,
      initializer_op=None,
      is_initialized_op=None,
      cached_value=None,
      save_slice_info=None,
      handle_deleter=None,
      caching_device=None,
      **unused_kwargs):
    """Creates a variable from a handle.

    Args:
      trainable: If `True`, GradientTapes automatically watch uses of this
        Variable.
      shape: The variable's shape.
      dtype: The variable's dtype.
      handle: The variable's handle
      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.
      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`.
      distribute_strategy: The distribution strategy this variable was created
        under.
      name: The name for this variable.
      unique_id: Internal. Unique ID for this variable's handle.
      handle_name: The name for the variable's handle.
      graph_element: Optional, required only in session.run-mode. Pre-created
        tensor which reads this variable's value.
      initial_value: Optional. Variable's initial value.
      initializer_op: Operation which assigns the variable's initial value.
      is_initialized_op: Pre-created operation to check whether this variable is
        initialized.
      cached_value: Pre-created operation to read this variable in a specific
        device.
      save_slice_info: Metadata for variable partitioning.
      handle_deleter: EagerResourceDeleter responsible for cleaning up the
        handle.
      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.
    """
    with ops.init_scope():
      self._in_graph_mode = not context.executing_eagerly()
    synchronization, aggregation, trainable = (
        variables.validate_synchronization_aggregation_trainable(
            synchronization, aggregation, trainable, name))
    self._trainable = trainable
    self._synchronization = synchronization
    self._aggregation = aggregation
    self._save_slice_info = save_slice_info
    self._initial_value = initial_value
    self._initializer_op = initializer_op
    self._is_initialized_op = is_initialized_op
    self._graph_element = graph_element
    self._caching_device = caching_device
    self._cached_value = cached_value
    self._distribute_strategy = distribute_strategy
    # Store the graph key so optimizers know how to only retrieve variables from
    # this graph. Guaranteed to be the same as the eager graph_key.
    self._graph_key = ops.get_default_graph()._graph_key  # pylint: disable=protected-access
    self._shape = tensor_shape.as_shape(shape)
    self._dtype = dtypes.as_dtype(dtype)
    self._handle = handle
    self._unique_id = unique_id
    self._handle_name = handle_name + ":0"
    self._constraint = constraint
    # After the handle has been created, set up a way to clean it up when
    # executing eagerly. We'll hold the only reference to the deleter, so that
    # when this object is garbage collected the deleter will be too. This
    # means ResourceVariables can be part of reference cycles without those
    # cycles being uncollectable.
    if not self._in_graph_mode:
      if handle_deleter is None:
        handle_deleter = EagerResourceDeleter(
            handle=self._handle, handle_device=self._handle.device)
    self._handle_deleter = handle_deleter
    self._cached_shape_as_list = None

  def __repr__(self):
    if context.executing_eagerly() and not self._in_graph_mode:
      # If we cannot read the value for any reason, still produce a __repr__.
      try:
        value_text = ops.numpy_text(self.read_value(), is_repr=True)
      except:  # pylint: disable=bare-except
        value_text = "<unavailable>"

      return "<tf.Variable '%s' shape=%s dtype=%s, numpy=%s>" % (
          self.name, self.get_shape(), self.dtype.name, value_text)
    else:
      return "<tf.Variable '%s' shape=%s dtype=%s>" % (
          self.name, self.get_shape(), self.dtype.name)

  @contextlib.contextmanager
  def _assign_dependencies(self):
    """Makes assignments depend on the cached value, if any.

    This prevents undefined behavior with reads not ordered wrt writes.

    Yields:
      None.
    """
    if self._cached_value is not None:
      with ops.control_dependencies([self._cached_value]):
        yield
    else:
      yield

  def __array__(self):
    """Allows direct conversion to a numpy array.

    >>> np.array(tf.Variable([1.0]))
    array([1.], dtype=float32)

    Returns:
      The variable value as a numpy array.
    """
    # You can't return `self.numpy()` here because for scalars
    # that raises:
    #     ValueError: object __array__ method not producing an array
    # Even `self.read_value().__array__()` and `self.read_value()._numpy()` give
    # the same error. The `EagerTensor` class must be doing something behind the
    # scenes to make `np.array(tf.constant(1))` work.
    return np.asarray(self.numpy())

  def __nonzero__(self):
    return self.__bool__()

  def __bool__(self):
    return bool(self.read_value())

  def __copy__(self):
    return self

  def __deepcopy__(self, memo):
    if not context.executing_eagerly():
      raise NotImplementedError(
          "__deepcopy__() is only available when eager execution is enabled.")
    copied_variable = ResourceVariable(
        initial_value=self.read_value(),
        trainable=self._trainable,
        constraint=self._constraint,
        dtype=self._dtype,
        name=self._shared_name,
        distribute_strategy=self._distribute_strategy,
        synchronization=self.synchronization,
        aggregation=self.aggregation)
    memo[self._unique_id] = copied_variable
    return copied_variable

  @property
  def dtype(self):
    """The dtype of this variable."""
    return self._dtype

  @property
  def device(self):
    """The device this variable is on."""
    return self._handle.device

  @property
  def graph(self):
    """The `Graph` of this variable."""
    return self._handle.graph

  @property
  def name(self):
    """The name of the handle for this variable."""
    return self._handle_name

  @property
  def shape(self):
    """The shape of this variable."""
    return self._shape

  def set_shape(self, shape):
    self._shape = self._shape.merge_with(shape)

  def _shape_as_list(self):
    if self.shape.ndims is None:
      return None
    return [dim.value for dim in self.shape.dims]

  def _shape_tuple(self):
    shape = self._shape_as_list()
    if shape is None:
      return None
    return tuple(shape)

  @property
  def create(self):
    """The op responsible for initializing this variable."""
    if not self._in_graph_mode:
      raise RuntimeError("Calling create is not supported when eager execution"
                         " is enabled.")
    return self._initializer_op

  @property
  def handle(self):
    """The handle by which this variable can be accessed."""
    return self._handle

  def value(self):
    """A cached operation which reads the value of this variable."""
    if self._cached_value is not None:
      return self._cached_value
    with ops.colocate_with(None, ignore_existing=True):
      return self._read_variable_op()

  def _as_graph_element(self):
    """Conversion function for Graph.as_graph_element()."""
    return self._graph_element

  @property
  def initializer(self):
    """The op responsible for initializing this variable."""
    return self._initializer_op

  @property
  def initial_value(self):
    """Returns the Tensor used as the initial value for the variable."""
    if context.executing_eagerly():
      raise RuntimeError("initial_value not supported in EAGER mode.")
    return self._initial_value

  @property
  def constraint(self):
    """Returns the constraint function associated with this variable.

    Returns:
      The constraint function that was passed to the variable constructor.
      Can be `None` if no constraint was passed.
    """
    return self._constraint

  @property
  def op(self):
    """The op for this variable."""
    return self._handle.op

  @property
  def trainable(self):
    return self._trainable

  @property
  def synchronization(self):
    return self._synchronization

  @property
  def aggregation(self):
    return self._aggregation

  def eval(self, session=None):
    """Evaluates and returns the value of this variable."""
    if context.executing_eagerly():
      raise RuntimeError("Trying to eval in EAGER mode")
    return self._graph_element.eval(session=session)

  def numpy(self):
    if context.executing_eagerly():
      return self.read_value().numpy()
    raise NotImplementedError(
        "numpy() is only available when eager execution is enabled.")

  @deprecated(None, "Prefer Dataset.range instead.")
  def count_up_to(self, limit):
    """Increments this variable until it reaches `limit`.

    When that Op is run it tries to increment the variable by `1`. If
    incrementing the variable would bring it above `limit` then the Op raises
    the exception `OutOfRangeError`.

    If no error is raised, the Op outputs the value of the variable before
    the increment.

    This is essentially a shortcut for `count_up_to(self, limit)`.

    Args:
      limit: value at which incrementing the variable raises an error.

    Returns:
      A `Tensor` that will hold the variable value before the increment. If no
      other Op modifies this variable, the values produced will all be
      distinct.
    """
    return gen_state_ops.resource_count_up_to(
        self.handle, limit=limit, T=self.dtype)

  def _map_resources(self, save_options):
    """For implementing `Trackable`."""
    new_variable = None
    if save_options.experimental_variable_policy._save_variable_devices():  # pylint:disable=protected-access
      with ops.device(self.device):
        new_variable = copy_to_graph_uninitialized(self)
    else:
      new_variable = copy_to_graph_uninitialized(self)
    obj_map = {self: new_variable}
    resource_map = {self._handle: new_variable.handle}
    return obj_map, resource_map

  def _read_variable_op(self):
    variable_accessed(self)

    def read_and_set_handle():
      result = gen_resource_variable_ops.read_variable_op(
          self._handle, self._dtype)
      _maybe_set_handle_data(self._dtype, self._handle, result)
      return result

    if getattr(self, "_caching_device", None) is not None:
      with ops.colocate_with(None, ignore_existing=True):
        with ops.device(self._caching_device):
          result = read_and_set_handle()
    else:
      result = read_and_set_handle()

    if not context.executing_eagerly():
      # Note that if a control flow context is active the input of the read op
      # might not actually be the handle. This line bypasses it.
      tape.record_operation(
          "ReadVariableOp", [result], [self._handle],
          backward_function=lambda x: [x],
          forward_function=lambda x: [x])
    return result

  def read_value(self):
    """Constructs an op which reads the value of this variable.

    Should be used when there are multiple reads, or when it is desirable to
    read the value only after some condition is true.

    Returns:
     the read operation.
    """
    with ops.name_scope("Read"):
      value = self._read_variable_op()
    # Return an identity so it can get placed on whatever device the context
    # specifies instead of the device where the variable is.
    return array_ops.identity(value)

  def sparse_read(self, indices, name=None):
    """Reads the value of this variable sparsely, using `gather`."""
    with ops.name_scope("Gather" if name is None else name) as name:
      variable_accessed(self)
      value = gen_resource_variable_ops.resource_gather(
          self._handle, indices, dtype=self._dtype, name=name)

      if self._dtype == dtypes.variant:
        # For DT_VARIANT types, the handle's shape_and_type[1:] stores the
        # variant's handle data.  Extract it.
        handle_data = get_eager_safe_handle_data(self._handle)
        if handle_data.is_set and len(handle_data.shape_and_type) > 1:
          value._handle_data = (  # pylint: disable=protected-access
              cpp_shape_inference_pb2.CppShapeInferenceResult.HandleData(
                  is_set=True, shape_and_type=handle_data.shape_and_type[1:]))

    return array_ops.identity(value)

  def gather_nd(self, indices, name=None):
    """Reads the value of this variable sparsely, using `gather_nd`."""
    with ops.name_scope("GatherNd" if name is None else name) as name:
      if self.trainable:
        variable_accessed(self)
      value = gen_resource_variable_ops.resource_gather_nd(
          self._handle, indices, dtype=self._dtype, name=name)

    return array_ops.identity(value)

  def to_proto(self, export_scope=None):
    """Converts a `ResourceVariable` to a `VariableDef` protocol buffer.

    Args:
      export_scope: Optional `string`. Name scope to remove.

    Raises:
      RuntimeError: If run in EAGER mode.

    Returns:
      A `VariableDef` protocol buffer, or `None` if the `Variable` is not
      in the specified name scope.
    """
    if context.executing_eagerly():
      raise RuntimeError("to_proto not supported in EAGER mode.")
    if export_scope is None or self.handle.name.startswith(export_scope):
      var_def = variable_pb2.VariableDef()
      var_def.variable_name = ops.strip_name_scope(self.handle.name,
                                                   export_scope)
      if self._initial_value is not None:
        # This is inside an if-statement for backwards compatibility, since
        # self._initial_value might be None for variables constructed from old
        # protos.
        var_def.initial_value_name = ops.strip_name_scope(
            self._initial_value.name, export_scope)
      var_def.initializer_name = ops.strip_name_scope(self.initializer.name,
                                                      export_scope)
      if self._cached_value is not None:
        var_def.snapshot_name = ops.strip_name_scope(self._cached_value.name,
                                                     export_scope)
      else:
        # Store the graph_element here
        var_def.snapshot_name = ops.strip_name_scope(self._graph_element.name,
                                                     export_scope)
      var_def.is_resource = True
      var_def.trainable = self.trainable
      var_def.synchronization = self.synchronization.value
      var_def.aggregation = self.aggregation.value
      if self._save_slice_info:
        var_def.save_slice_info_def.MergeFrom(
            self._save_slice_info.to_proto(export_scope=export_scope))
      return var_def
    else:
      return None

  @staticmethod
  def from_proto(variable_def, import_scope=None):
    if context.executing_eagerly():
      raise RuntimeError("from_proto not supported in EAGER mode.")
    return ResourceVariable(
        variable_def=variable_def, import_scope=import_scope)

  __array_priority__ = 100

  def is_initialized(self, name=None):
    """Checks whether a resource variable has been initialized.

    Outputs boolean scalar indicating whether the tensor has been initialized.

    Args:
      name: A name for the operation (optional).

    Returns:
      A `Tensor` of type `bool`.
    """
    # TODO(b/169792703): The current device placement logic never overrides an
    # explicit placement with a custom device, causing `v.is_initalized()` to
    # fail under a non-custom device context if `v` is in a custom device. The
    # explicit placement below makes this work, but should not be necessary once
    # the logic is updated to handle cases like this.
    with ops.device(self.device):
      return gen_resource_variable_ops.var_is_initialized_op(self.handle, name)

  def assign_sub(self, delta, use_locking=None, name=None, read_value=True):
    """Subtracts a value from this variable.

    Args:
      delta: A `Tensor`. The value to subtract from this variable.
      use_locking: If `True`, use locking during the operation.
      name: The name to use for the operation.
      read_value: A `bool`. Whether to read and return the new value of the
        variable or not.

    Returns:
      If `read_value` is `True`, this method will return the new value of the
      variable after the assignment has completed. Otherwise, when in graph mode
      it will return the `Operation` that does the assignment, and when in eager
      mode it will return `None`.
    """
    # TODO(apassos): this here and below is not atomic. Consider making it
    # atomic if there's a way to do so without a performance cost for those who
    # don't need it.
    with _handle_graph(self.handle), self._assign_dependencies():
      assign_sub_op = gen_resource_variable_ops.assign_sub_variable_op(
          self.handle,
          ops.convert_to_tensor(delta, dtype=self.dtype),
          name=name)
    if read_value:
      return self._lazy_read(assign_sub_op)
    return assign_sub_op

  def assign_add(self, delta, use_locking=None, name=None, read_value=True):
    """Adds a value to this variable.

    Args:
      delta: A `Tensor`. The value to add to this variable.
      use_locking: If `True`, use locking during the operation.
      name: The name to use for the operation.
      read_value: A `bool`. Whether to read and return the new value of the
        variable or not.

    Returns:
      If `read_value` is `True`, this method will return the new value of the
      variable after the assignment has completed. Otherwise, when in graph mode
      it will return the `Operation` that does the assignment, and when in eager
      mode it will return `None`.
    """
    with _handle_graph(self.handle), self._assign_dependencies():
      assign_add_op = gen_resource_variable_ops.assign_add_variable_op(
          self.handle,
          ops.convert_to_tensor(delta, dtype=self.dtype),
          name=name)
    if read_value:
      return self._lazy_read(assign_add_op)
    return assign_add_op

  def _lazy_read(self, op):
    variable_accessed(self)
    return _UnreadVariable(
        handle=self._handle,
        dtype=self.dtype,
        shape=self._shape,
        in_graph_mode=self._in_graph_mode,
        deleter=self._handle_deleter if not self._in_graph_mode else None,
        parent_op=op,
        unique_id=self._unique_id)

  def assign(self, value, use_locking=None, name=None, read_value=True):
    """Assigns a new value to this variable.

    Args:
      value: A `Tensor`. The new value for this variable.
      use_locking: If `True`, use locking during the assignment.
      name: The name to use for the assignment.
      read_value: A `bool`. Whether to read and return the new value of the
        variable or not.

    Returns:
      If `read_value` is `True`, this method will return the new value of the
      variable after the assignment has completed. Otherwise, when in graph mode
      it will return the `Operation` that does the assignment, and when in eager
      mode it will return `None`.
    """
    # Note: not depending on the cached value here since this can be used to
    # initialize the variable.
    with _handle_graph(self.handle):
      value_tensor = ops.convert_to_tensor(value, dtype=self.dtype)
      if not self._shape.is_compatible_with(value_tensor.shape):
        if self.name is None:
          tensor_name = ""
        else:
          tensor_name = " " + str(self.name)
        raise ValueError(
            ("Cannot assign to variable%s due to variable shape %s and value "
             "shape %s are incompatible") %
            (tensor_name, self._shape, value_tensor.shape))
      assign_op = gen_resource_variable_ops.assign_variable_op(
          self.handle, value_tensor, name=name)
      if read_value:
        return self._lazy_read(assign_op)
    return assign_op

  def __reduce__(self):
    # The implementation mirrors that of __deepcopy__.
    return functools.partial(
        ResourceVariable,
        initial_value=self.numpy(),
        trainable=self.trainable,
        name=self._shared_name,
        dtype=self.dtype,
        constraint=self.constraint,
        distribute_strategy=self._distribute_strategy), ()

  def scatter_sub(self, sparse_delta, use_locking=False, name=None):
    """Subtracts `tf.IndexedSlices` from this variable.

    Args:
      sparse_delta: `tf.IndexedSlices` to be subtracted from this variable.
      use_locking: If `True`, use locking during the operation.
      name: the name of the operation.

    Returns:
      The updated variable.

    Raises:
      TypeError: if `sparse_delta` is not an `IndexedSlices`.
    """
    if not isinstance(sparse_delta, ops.IndexedSlices):
      raise TypeError("sparse_delta is not IndexedSlices: %s" % sparse_delta)
    return self._lazy_read(
        gen_resource_variable_ops.resource_scatter_sub(
            self.handle,
            sparse_delta.indices,
            ops.convert_to_tensor(sparse_delta.values, self.dtype),
            name=name))

  def scatter_add(self, sparse_delta, use_locking=False, name=None):
    """Adds `tf.IndexedSlices` to this variable.

    Args:
      sparse_delta: `tf.IndexedSlices` to be added to this variable.
      use_locking: If `True`, use locking during the operation.
      name: the name of the operation.

    Returns:
      The updated variable.

    Raises:
      TypeError: if `sparse_delta` is not an `IndexedSlices`.
    """
    if not isinstance(sparse_delta, ops.IndexedSlices):
      raise TypeError("sparse_delta is not IndexedSlices: %s" % sparse_delta)
    return self._lazy_read(
        gen_resource_variable_ops.resource_scatter_add(
            self.handle,
            sparse_delta.indices,
            ops.convert_to_tensor(sparse_delta.values, self.dtype),
            name=name))

  def scatter_max(self, sparse_delta, use_locking=False, name=None):
    """Updates this variable with the max of `tf.IndexedSlices` and itself.

    Args:
      sparse_delta: `tf.IndexedSlices` to use as an argument of max with this
        variable.
      use_locking: If `True`, use locking during the operation.
      name: the name of the operation.

    Returns:
      The updated variable.

    Raises:
      TypeError: if `sparse_delta` is not an `IndexedSlices`.
    """
    if not isinstance(sparse_delta, ops.IndexedSlices):
      raise TypeError("sparse_delta is not IndexedSlices: %s" % sparse_delta)
    return self._lazy_read(
        gen_resource_variable_ops.resource_scatter_max(
            self.handle,
            sparse_delta.indices,
            ops.convert_to_tensor(sparse_delta.values, self.dtype),
            name=name))

  def scatter_min(self, sparse_delta, use_locking=False, name=None):
    """Updates this variable with the min of `tf.IndexedSlices` and itself.

    Args:
      sparse_delta: `tf.IndexedSlices` to use as an argument of min with this
        variable.
      use_locking: If `True`, use locking during the operation.
      name: the name of the operation.

    Returns:
      The updated variable.

    Raises:
      TypeError: if `sparse_delta` is not an `IndexedSlices`.
    """
    if not isinstance(sparse_delta, ops.IndexedSlices):
      raise TypeError("sparse_delta is not IndexedSlices: %s" % sparse_delta)
    return self._lazy_read(
        gen_resource_variable_ops.resource_scatter_min(
            self.handle,
            sparse_delta.indices,
            ops.convert_to_tensor(sparse_delta.values, self.dtype),
            name=name))

  def scatter_mul(self, sparse_delta, use_locking=False, name=None):
    """Multiply this variable by `tf.IndexedSlices`.

    Args:
      sparse_delta: `tf.IndexedSlices` to multiply this variable by.
      use_locking: If `True`, use locking during the operation.
      name: the name of the operation.

    Returns:
      The updated variable.

    Raises:
      TypeError: if `sparse_delta` is not an `IndexedSlices`.
    """
    if not isinstance(sparse_delta, ops.IndexedSlices):
      raise TypeError("sparse_delta is not IndexedSlices: %s" % sparse_delta)
    return self._lazy_read(
        gen_resource_variable_ops.resource_scatter_mul(
            self.handle,
            sparse_delta.indices,
            ops.convert_to_tensor(sparse_delta.values, self.dtype),
            name=name))

  def scatter_div(self, sparse_delta, use_locking=False, name=None):
    """Divide this variable by `tf.IndexedSlices`.

    Args:
      sparse_delta: `tf.IndexedSlices` to divide this variable by.
      use_locking: If `True`, use locking during the operation.
      name: the name of the operation.

    Returns:
      The updated variable.

    Raises:
      TypeError: if `sparse_delta` is not an `IndexedSlices`.
    """
    if not isinstance(sparse_delta, ops.IndexedSlices):
      raise TypeError("sparse_delta is not IndexedSlices: %s" % sparse_delta)
    return self._lazy_read(
        gen_resource_variable_ops.resource_scatter_div(
            self.handle,
            sparse_delta.indices,
            ops.convert_to_tensor(sparse_delta.values, self.dtype),
            name=name))

  def scatter_update(self, sparse_delta, use_locking=False, name=None):
    """Assigns `tf.IndexedSlices` to this variable.

    Args:
      sparse_delta: `tf.IndexedSlices` to be assigned to this variable.
      use_locking: If `True`, use locking during the operation.
      name: the name of the operation.

    Returns:
      The updated variable.

    Raises:
      TypeError: if `sparse_delta` is not an `IndexedSlices`.
    """
    if not isinstance(sparse_delta, ops.IndexedSlices):
      raise TypeError("sparse_delta is not IndexedSlices: %s" % sparse_delta)
    return self._lazy_read(
        gen_resource_variable_ops.resource_scatter_update(
            self.handle,
            sparse_delta.indices,
            ops.convert_to_tensor(sparse_delta.values, self.dtype),
            name=name))

  def batch_scatter_update(self, sparse_delta, use_locking=False, name=None):
    """Assigns `tf.IndexedSlices` to this variable batch-wise.

    Analogous to `batch_gather`. This assumes that this variable and the
    sparse_delta IndexedSlices have a series of leading dimensions that are the
    same for all of them, and the updates are performed on the last dimension of
    indices. In other words, the dimensions should be the following:

    `num_prefix_dims = sparse_delta.indices.ndims - 1`
    `batch_dim = num_prefix_dims + 1`
    `sparse_delta.updates.shape = sparse_delta.indices.shape + var.shape[
         batch_dim:]`

    where

    `sparse_delta.updates.shape[:num_prefix_dims]`
    `== sparse_delta.indices.shape[:num_prefix_dims]`
    `== var.shape[:num_prefix_dims]`

    And the operation performed can be expressed as:

    `var[i_1, ..., i_n,
         sparse_delta.indices[i_1, ..., i_n, j]] = sparse_delta.updates[
            i_1, ..., i_n, j]`

    When sparse_delta.indices is a 1D tensor, this operation is equivalent to
    `scatter_update`.

    To avoid this operation one can looping over the first `ndims` of the
    variable and using `scatter_update` on the subtensors that result of slicing
    the first dimension. This is a valid option for `ndims = 1`, but less
    efficient than this implementation.

    Args:
      sparse_delta: `tf.IndexedSlices` to be assigned to this variable.
      use_locking: If `True`, use locking during the operation.
      name: the name of the operation.

    Returns:
      The updated variable.

    Raises:
      TypeError: if `sparse_delta` is not an `IndexedSlices`.
    """
    if not isinstance(sparse_delta, ops.IndexedSlices):
      raise TypeError("sparse_delta is not IndexedSlices: %s" % sparse_delta)
    return self._lazy_read(
        state_ops.batch_scatter_update(
            self,
            sparse_delta.indices,
            sparse_delta.values,
            use_locking=use_locking,
            name=name))

  def scatter_nd_sub(self, indices, updates, name=None):
    """Applies sparse subtraction to individual values or slices in a Variable.

    `ref` is a `Tensor` with rank `P` and `indices` is a `Tensor` of rank `Q`.

    `indices` must be integer tensor, containing indices into `ref`.
    It must be shape `[d_0, ..., d_{Q-2}, K]` where `0 < K <= P`.

    The innermost dimension of `indices` (with length `K`) corresponds to
    indices into elements (if `K = P`) or slices (if `K < P`) along the `K`th
    dimension of `ref`.

    `updates` is `Tensor` of rank `Q-1+P-K` with shape:

    ```
    [d_0, ..., d_{Q-2}, ref.shape[K], ..., ref.shape[P-1]].
    ```

    For example, say we want to add 4 scattered elements to a rank-1 tensor to
    8 elements. In Python, that update would look like this:

    ```python
        ref = tf.Variable([1, 2, 3, 4, 5, 6, 7, 8])
        indices = tf.constant([[4], [3], [1] ,[7]])
        updates = tf.constant([9, 10, 11, 12])
        op = ref.scatter_nd_sub(indices, updates)
        with tf.compat.v1.Session() as sess:
          print sess.run(op)
    ```

    The resulting update to ref would look like this:

        [1, -9, 3, -6, -6, 6, 7, -4]

    See `tf.scatter_nd` for more details about how to make updates to
    slices.

    Args:
      indices: The indices to be used in the operation.
      updates: The values to be used in the operation.
      name: the name of the operation.

    Returns:
      The updated variable.
    """
    return self._lazy_read(
        gen_state_ops.resource_scatter_nd_sub(
            self.handle,
            indices,
            ops.convert_to_tensor(updates, self.dtype),
            name=name))

  def scatter_nd_add(self, indices, updates, name=None):
    """Applies sparse addition to individual values or slices in a Variable.

    `ref` is a `Tensor` with rank `P` and `indices` is a `Tensor` of rank `Q`.

    `indices` must be integer tensor, containing indices into `ref`.
    It must be shape `[d_0, ..., d_{Q-2}, K]` where `0 < K <= P`.

    The innermost dimension of `indices` (with length `K`) corresponds to
    indices into elements (if `K = P`) or slices (if `K < P`) along the `K`th
    dimension of `ref`.

    `updates` is `Tensor` of rank `Q-1+P-K` with shape:

    ```
    [d_0, ..., d_{Q-2}, ref.shape[K], ..., ref.shape[P-1]].
    ```

    For example, say we want to add 4 scattered elements to a rank-1 tensor to
    8 elements. In Python, that update would look like this:

    ```python
        ref = tf.Variable([1, 2, 3, 4, 5, 6, 7, 8])
        indices = tf.constant([[4], [3], [1] ,[7]])
        updates = tf.constant([9, 10, 11, 12])
        add = ref.scatter_nd_add(indices, updates)
        with tf.compat.v1.Session() as sess:
          print sess.run(add)
    ```

    The resulting update to ref would look like this:

        [1, 13, 3, 14, 14, 6, 7, 20]

    See `tf.scatter_nd` for more details about how to make updates to
    slices.

    Args:
      indices: The indices to be used in the operation.
      updates: The values to be used in the operation.
      name: the name of the operation.

    Returns:
      The updated variable.
    """
    return self._lazy_read(
        gen_state_ops.resource_scatter_nd_add(
            self.handle,
            indices,
            ops.convert_to_tensor(updates, self.dtype),
            name=name))

  def scatter_nd_update(self, indices, updates, name=None):
    """Applies sparse assignment to individual values or slices in a Variable.

    `ref` is a `Tensor` with rank `P` and `indices` is a `Tensor` of rank `Q`.

    `indices` must be integer tensor, containing indices into `ref`.
    It must be shape `[d_0, ..., d_{Q-2}, K]` where `0 < K <= P`.

    The innermost dimension of `indices` (with length `K`) corresponds to
    indices into elements (if `K = P`) or slices (if `K < P`) along the `K`th
    dimension of `ref`.

    `updates` is `Tensor` of rank `Q-1+P-K` with shape:

    ```
    [d_0, ..., d_{Q-2}, ref.shape[K], ..., ref.shape[P-1]].
    ```

    For example, say we want to add 4 scattered elements to a rank-1 tensor to
    8 elements. In Python, that update would look like this:

    ```python
        ref = tf.Variable([1, 2, 3, 4, 5, 6, 7, 8])
        indices = tf.constant([[4], [3], [1] ,[7]])
        updates = tf.constant([9, 10, 11, 12])
        op = ref.scatter_nd_update(indices, updates)
        with tf.compat.v1.Session() as sess:
          print sess.run(op)
    ```

    The resulting update to ref would look like this:

        [1, 11, 3, 10, 9, 6, 7, 12]

    See `tf.scatter_nd` for more details about how to make updates to
    slices.

    Args:
      indices: The indices to be used in the operation.
      updates: The values to be used in the operation.
      name: the name of the operation.

    Returns:
      The updated variable.
    """
    return self._lazy_read(
        gen_state_ops.resource_scatter_nd_update(
            self.handle,
            indices,
            ops.convert_to_tensor(updates, self.dtype),
            name=name))

  def scatter_nd_max(self, indices, updates, name=None):
    """Updates this variable with the max of `tf.IndexedSlices` and itself.

    `ref` is a `Tensor` with rank `P` and `indices` is a `Tensor` of rank `Q`.

    `indices` must be integer tensor, containing indices into `ref`.
    It must be shape `[d_0, ..., d_{Q-2}, K]` where `0 < K <= P`.

    The innermost dimension of `indices` (with length `K`) corresponds to
    indices into elements (if `K = P`) or slices (if `K < P`) along the `K`th
    dimension of `ref`.

    `updates` is `Tensor` of rank `Q-1+P-K` with shape:

    ```
    [d_0, ..., d_{Q-2}, ref.shape[K], ..., ref.shape[P-1]].
    ```

    See `tf.scatter_nd` for more details about how to make updates to
    slices.

    Args:
      indices: The indices to be used in the operation.
      updates: The values to be used in the operation.
      name: the name of the operation.

    Returns:
      The updated variable.
    """
    return self._lazy_read(
        gen_state_ops.resource_scatter_nd_max(
            self.handle,
            indices,
            ops.convert_to_tensor(updates, self.dtype),
            name=name))

  def scatter_nd_min(self, indices, updates, name=None):
    """Updates this variable with the min of `tf.IndexedSlices` and itself.

    `ref` is a `Tensor` with rank `P` and `indices` is a `Tensor` of rank `Q`.

    `indices` must be integer tensor, containing indices into `ref`.
    It must be shape `[d_0, ..., d_{Q-2}, K]` where `0 < K <= P`.

    The innermost dimension of `indices` (with length `K`) corresponds to
    indices into elements (if `K = P`) or slices (if `K < P`) along the `K`th
    dimension of `ref`.

    `updates` is `Tensor` of rank `Q-1+P-K` with shape:

    ```
    [d_0, ..., d_{Q-2}, ref.shape[K], ..., ref.shape[P-1]].
    ```

    See `tf.scatter_nd` for more details about how to make updates to
    slices.

    Args:
      indices: The indices to be used in the operation.
      updates: The values to be used in the operation.
      name: the name of the operation.

    Returns:
      The updated variable.
    """
    return self._lazy_read(
        gen_state_ops.resource_scatter_nd_min(
            self.handle,
            indices,
            ops.convert_to_tensor(updates, self.dtype),
            name=name))

  def _strided_slice_assign(self, begin, end, strides, value, name, begin_mask,
                            end_mask, ellipsis_mask, new_axis_mask,
                            shrink_axis_mask):
    with _handle_graph(self.handle), self._assign_dependencies():
      return self._lazy_read(
          gen_array_ops.resource_strided_slice_assign(
              ref=self.handle,
              begin=begin,
              end=end,
              strides=strides,
              value=ops.convert_to_tensor(value, dtype=self.dtype),
              name=name,
              begin_mask=begin_mask,
              end_mask=end_mask,
              ellipsis_mask=ellipsis_mask,
              new_axis_mask=new_axis_mask,
              shrink_axis_mask=shrink_axis_mask))

  def __complex__(self):
    return complex(self.value().numpy())

  def __int__(self):
    return int(self.value().numpy())

  def __long__(self):
    return long(self.value().numpy())

  def __float__(self):
    return float(self.value().numpy())

  def _dense_var_to_tensor(self, dtype=None, name=None, as_ref=False):
    del name
    if dtype is not None and not dtype.is_compatible_with(self.dtype):
      raise ValueError(
          "Incompatible type conversion requested to type {!r} for variable "
          "of type {!r}".format(dtype.name, self.dtype.name))
    if as_ref:
      return self.read_value().op.inputs[0]
    else:
      return self.value()

  def __iadd__(self, unused_other):
    raise RuntimeError("Variable += value not supported. Use "
                       "variable.assign_add(value) to modify the variable "
                       "value and variable = variable + value to get a new "
                       "Tensor object.")

  def __isub__(self, unused_other):
    raise RuntimeError("Variable -= value not supported. Use "
                       "variable.assign_sub(value) to modify the variable "
                       "value and variable = variable - value to get a new "
                       "Tensor object.")

  def __imul__(self, unused_other):
    raise RuntimeError("Variable *= value not supported. Use "
                       "`var.assign(var * value)` to modify the variable or "
                       "`var = var * value` to get a new Tensor object.")

  def __idiv__(self, unused_other):
    raise RuntimeError("Variable /= value not supported. Use "
                       "`var.assign(var / value)` to modify the variable or "
                       "`var = var / value` to get a new Tensor object.")

  def __itruediv__(self, unused_other):
    raise RuntimeError("Variable /= value not supported. Use "
                       "`var.assign(var / value)` to modify the variable or "
                       "`var = var / value` to get a new Tensor object.")

  def __irealdiv__(self, unused_other):
    raise RuntimeError("Variable /= value not supported. Use "
                       "`var.assign(var / value)` to modify the variable or "
                       "`var = var / value` to get a new Tensor object.")

  def __ipow__(self, unused_other):
    raise RuntimeError("Variable **= value not supported. Use "
                       "`var.assign(var ** value)` to modify the variable or "
                       "`var = var ** value` to get a new Tensor object.")


class ResourceVariable(BaseResourceVariable):
  """Variable based on resource handles.

  See the [Variables How To](https://tensorflow.org/guide/variables)
  for a high level overview.

  A `ResourceVariable` allows you to maintain state across subsequent calls to
  session.run.

  The `ResourceVariable` constructor requires an initial value for the variable,
  which can be a `Tensor` of any type and shape. The initial value defines the
  type and shape of the variable. After construction, the type and shape of
  the variable are fixed. The value can be changed using one of the assign
  methods.

  Just like any `Tensor`, variables created with
  `tf.Variable(use_resource=True)` can be used as inputs for other Ops in the
  graph. Additionally, all the operators overloaded for the `Tensor` class are
  carried over to variables, so you can also add nodes to the graph by just
  doing arithmetic on variables.

  Unlike ref-based variable, a ResourceVariable has well-defined semantics. Each
  usage of a ResourceVariable in a TensorFlow graph adds a read_value operation
  to the graph. The Tensors returned by a read_value operation are guaranteed to
  see all modifications to the value of the variable which happen in any
  operation on which the read_value depends on (either directly, indirectly, or
  via a control dependency) and guaranteed to not see any modification to the
  value of the variable from operations that depend on the read_value operation.
  Updates from operations that have no dependency relationship to the read_value
  operation might or might not be visible to read_value.

  For example, if there is more than one assignment to a ResourceVariable in
  a single session.run call there is a well-defined value for each operation
  which uses the variable's value if the assignments and the read are connected
  by edges in the graph. Consider the following example, in which two writes
  can cause tf.Variable and tf.ResourceVariable to behave differently:

  ```python
  a = tf.Variable(1.0, use_resource=True)
  a.initializer.run()

  assign = a.assign(2.0)
  with tf.control_dependencies([assign]):
    b = a.read_value()
  with tf.control_dependencies([b]):
    other_assign = a.assign(3.0)
  with tf.control_dependencies([other_assign]):
    # Will print 2.0 because the value was read before other_assign ran. If
    # `a` was a tf.Variable instead, 2.0 or 3.0 could be printed.
    tf.compat.v1.Print(b, [b]).eval()
  ```
  """

  def __init__(
      self,  # pylint: disable=super-init-not-called
      initial_value=None,
      trainable=None,
      collections=None,
      validate_shape=True,  # pylint: disable=unused-argument
      caching_device=None,
      name=None,
      dtype=None,
      variable_def=None,
      import_scope=None,
      constraint=None,
      distribute_strategy=None,
      synchronization=None,
      aggregation=None,
      shape=None):
    """Creates a variable.

    Args:
      initial_value: A `Tensor`, or Python object convertible to a `Tensor`,
        which is the initial value for the Variable. 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`, the default, also adds the variable to the graph
        collection `GraphKeys.TRAINABLE_VARIABLES`. This collection is used as
        the default list of variables to use by the `Optimizer` classes.
        Defaults to `True`, unless `synchronization` is set to `ON_READ`, in
        which case it defaults to `False`.
      collections: List of graph collections keys. The new variable is added to
        these collections. Defaults to `[GraphKeys.GLOBAL_VARIABLES]`.
      validate_shape: Ignored. Provided for compatibility with tf.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).
      variable_def: `VariableDef` protocol buffer. If not None, recreates the
        `ResourceVariable` object with its contents. `variable_def` and other
        arguments (except for import_scope) are mutually exclusive.
      import_scope: Optional `string`. Name scope to add to the
        ResourceVariable. Only used when `variable_def` is provided.
      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.
      distribute_strategy: The tf.distribute.Strategy this variable is being
        created inside of.
      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`.

    @compatibility(eager)
    When Eager Execution is enabled, the default for the `collections` argument
    is `None`, which signifies that this `Variable` will not be added to any
    collections.
    @end_compatibility
    """
    if variable_def:
      if initial_value is not None:
        raise ValueError("variable_def and initial_value are mutually "
                         "exclusive.")
      if context.executing_eagerly():
        raise ValueError("Creating ResourceVariable from variable_def is "
                         "not supported when eager execution is enabled.")
      self._init_from_proto(variable_def, import_scope=import_scope)
    else:
      self._init_from_args(
          initial_value=initial_value,
          trainable=trainable,
          collections=collections,
          caching_device=caching_device,
          name=name,
          dtype=dtype,
          constraint=constraint,
          synchronization=synchronization,
          aggregation=aggregation,
          shape=shape,
          distribute_strategy=distribute_strategy)

  def _init_from_args(self,
                      initial_value=None,
                      trainable=None,
                      collections=None,
                      caching_device=None,
                      name=None,
                      dtype=None,
                      constraint=None,
                      synchronization=None,
                      aggregation=None,
                      distribute_strategy=None,
                      shape=None):
    """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`, the default, also adds the variable to the graph
        collection `GraphKeys.TRAINABLE_VARIABLES`. This collection is used as
        the default list of variables to use by the `Optimizer` classes.
        Defaults to `True`, unless `synchronization` is set to `ON_READ`, in
        which case it defaults to `False`.
      collections: List of graph collections keys. The new variable is added to
        these collections. Defaults to `[GraphKeys.GLOBAL_VARIABLES]`.
      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.
      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`.
      distribute_strategy: DistributionStrategy under which this variable was
        created.
      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`.

    @compatibility(eager)
    When Eager Execution is enabled, variables are never added to collections.
    It is not implicitly added to the `GLOBAL_VARIABLES` or
    `TRAINABLE_VARIABLES` collections, and the `collections` argument is
    ignored.
    @end_compatibility
    """
    synchronization, aggregation, trainable = (
        variables.validate_synchronization_aggregation_trainable(
            synchronization, aggregation, trainable, name))
    if initial_value is None:
      raise ValueError("initial_value must be specified.")
    init_from_fn = callable(initial_value)

    if isinstance(initial_value, ops.Tensor) and hasattr(
        initial_value, "graph") and initial_value.graph.building_function:
      raise ValueError("Tensor-typed variable initializers must either be "
                       "wrapped in an init_scope or callable "
                       "(e.g., `tf.Variable(lambda : "
                       "tf.truncated_normal([10, 40]))`) when building "
                       "functions. Please file a feature request if this "
                       "restriction inconveniences you.")

    if collections is None:
      collections = [ops.GraphKeys.GLOBAL_VARIABLES]
    if not isinstance(collections, (list, tuple, set)):
      raise ValueError(
          "collections argument to Variable constructor must be a list, tuple, "
          "or set. Got %s of type %s" % (collections, type(collections)))
    if constraint is not None and not callable(constraint):
      raise ValueError("The `constraint` argument must be a callable.")

    if trainable and ops.GraphKeys.TRAINABLE_VARIABLES not in collections:
      collections = list(collections) + [ops.GraphKeys.TRAINABLE_VARIABLES]
    with ops.init_scope():
      self._in_graph_mode = not context.executing_eagerly()
      with ops.name_scope(
          name,
          "Variable", [] if init_from_fn else [initial_value],
          skip_on_eager=False) as name:
        # pylint: disable=protected-access
        handle_name = ops.name_from_scope_name(name)
        if self._in_graph_mode:
          shared_name = handle_name
          unique_id = shared_name
        else:
          # When in eager mode use a uid for the shared_name, to prevent
          # accidental sharing.
          unique_id = "%s_%d" % (handle_name, ops.uid())
          shared_name = None  # Never shared
        # Use attr_scope and device(None) to simulate the behavior of
        # colocate_with when the variable we want to colocate with doesn't
        # yet exist.
        device_context_manager = (
            ops.device if self._in_graph_mode else ops.NullContextmanager)
        attr = attr_value_pb2.AttrValue(
            list=attr_value_pb2.AttrValue.ListValue(
                s=[compat.as_bytes("loc:@%s" % handle_name)]))
        with ops.get_default_graph()._attr_scope({"_class": attr}):
          with ops.name_scope("Initializer"), device_context_manager(None):
            if init_from_fn:
              initial_value = initial_value()
            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
            initial_value = ops.convert_to_tensor(initial_value,
                                                  name="initial_value",
                                                  dtype=dtype)
          if shape is not None:
            if not initial_value.shape.is_compatible_with(shape):
              raise ValueError(
                  "The initial value's shape (%s) is not compatible with "
                  "the explicitly supplied `shape` argument (%s)." %
                  (initial_value.shape, shape))
          else:
            shape = initial_value.shape
          handle = eager_safe_variable_handle(
              initial_value=initial_value,
              shape=shape,
              shared_name=shared_name,
              name=name,
              graph_mode=self._in_graph_mode)
        # pylint: disable=protected-access
        if (self._in_graph_mode and initial_value is not None and
            initial_value.op._get_control_flow_context() is not None):
          raise ValueError(
              "Initializer for variable %s is from inside a control-flow "
              "construct, such as a loop or conditional. When creating a "
              "variable inside a loop or conditional, use a lambda as the "
              "initializer." % name)
        # pylint: enable=protected-access
        dtype = initial_value.dtype.base_dtype

        if self._in_graph_mode:
          with ops.name_scope("IsInitialized"):
            is_initialized_op = (
                gen_resource_variable_ops.var_is_initialized_op(handle))
          if initial_value is not None:
            # pylint: disable=g-backslash-continuation
            with ops.name_scope("Assign") as n, \
                 ops.colocate_with(None, ignore_existing=True), \
                 ops.device(handle.device):
              # pylint: disable=protected-access
              initializer_op = (
                  gen_resource_variable_ops.assign_variable_op(
                      handle,
                      variables._try_guard_against_uninitialized_dependencies(
                          name, initial_value),
                      name=n))
              # pylint: enable=protected-access
            # pylint: enable=g-backslash-continuation
          with ops.name_scope("Read"):
            # Manually assign reads to the handle's device to avoid log
            # messages.
            with ops.device(handle.device):
              value = gen_resource_variable_ops.read_variable_op(handle, dtype)
              _maybe_set_handle_data(dtype, handle, value)
            graph_element = value
            if caching_device is not None:
              # Variables may be created in a tf.device() or ops.colocate_with()
              # context. At the same time, users would expect caching device to
              # be independent of this context, and/or would not expect the
              # current device context to be merged with the caching device
              # spec.  Therefore we reset the colocation stack before creating
              # the cached value. Note that resetting the colocation stack will
              # also reset the device stack.
              with ops.colocate_with(None, ignore_existing=True):
                with ops.device(caching_device):
                  cached_value = array_ops.identity(value)
            else:
              cached_value = None
        else:
          gen_resource_variable_ops.assign_variable_op(handle, initial_value)
          is_initialized_op = None
          initializer_op = None
          graph_element = None
          if caching_device:
            with ops.device(caching_device):
              cached_value = gen_resource_variable_ops.read_variable_op(
                  handle, dtype)
              _maybe_set_handle_data(dtype, handle, cached_value)
          else:
            cached_value = None

        if cached_value is not None:
          # Store the variable object so that the original variable can be
          # accessed to generate functions that are compatible with SavedModel.
          cached_value._cached_variable = weakref.ref(self)  # pylint: disable=protected-access

        if not context.executing_eagerly():
          # Eager variables are only added to collections if they are part of an
          # eager variable store (otherwise in an interactive session they would
          # hog memory and cause OOM). This is done in ops/variable_scope.py.
          ops.add_to_collections(collections, self)
        elif ops.GraphKeys.GLOBAL_STEP in collections:
          ops.add_to_collections(ops.GraphKeys.GLOBAL_STEP, self)
      initial_value = initial_value if self._in_graph_mode else None
      super(ResourceVariable, self).__init__(
          trainable=trainable,
          shape=shape,
          dtype=dtype,
          handle=handle,
          synchronization=synchronization,
          constraint=constraint,
          aggregation=aggregation,
          distribute_strategy=distribute_strategy,
          name=name,
          unique_id=unique_id,
          handle_name=handle_name,
          graph_element=graph_element,
          initial_value=initial_value,
          initializer_op=initializer_op,
          is_initialized_op=is_initialized_op,
          cached_value=cached_value,
          caching_device=caching_device)

  def _init_from_proto(self, variable_def, import_scope=None):
    """Initializes from `VariableDef` proto."""
    # Note that init_from_proto is currently not supported in Eager mode.
    assert not context.executing_eagerly()
    self._in_graph_mode = True
    assert isinstance(variable_def, variable_pb2.VariableDef)
    if not variable_def.is_resource:
      raise ValueError("Trying to restore Variable as ResourceVariable.")

    # Create from variable_def.
    g = ops.get_default_graph()
    self._handle = g.as_graph_element(
        ops.prepend_name_scope(
            variable_def.variable_name, import_scope=import_scope))
    self._shape = tensor_shape.TensorShape(self._handle.op.get_attr("shape"))
    self._handle_name = self._handle.name
    self._unique_id = self._handle_name
    self._initializer_op = g.as_graph_element(
        ops.prepend_name_scope(
            variable_def.initializer_name, import_scope=import_scope))
    # Check whether initial_value_name exists for backwards compatibility.
    if (hasattr(variable_def, "initial_value_name") and
        variable_def.initial_value_name):
      self._initial_value = g.as_graph_element(
          ops.prepend_name_scope(
              variable_def.initial_value_name, import_scope=import_scope))
    else:
      self._initial_value = None
    synchronization, aggregation, trainable = (
        variables.validate_synchronization_aggregation_trainable(
            variable_def.synchronization, variable_def.aggregation,
            variable_def.trainable, variable_def.variable_name))
    self._synchronization = synchronization
    self._aggregation = aggregation
    self._trainable = trainable
    if variable_def.snapshot_name:
      snapshot = g.as_graph_element(
          ops.prepend_name_scope(
              variable_def.snapshot_name, import_scope=import_scope))
      if snapshot.op.type != "ReadVariableOp":
        self._cached_value = snapshot
      else:
        self._cached_value = None
      while snapshot.op.type != "ReadVariableOp":
        snapshot = snapshot.op.inputs[0]
      self._graph_element = snapshot
    else:
      self._cached_value = None
      # Legacy case for protos without the snapshot name; assume it's the
      # following.
      self._graph_element = g.get_tensor_by_name(self._handle.op.name +
                                                 "/Read/ReadVariableOp:0")
    if variable_def.HasField("save_slice_info_def"):
      self._save_slice_info = variables.Variable.SaveSliceInfo(
          save_slice_info_def=variable_def.save_slice_info_def,
          import_scope=import_scope)
    else:
      self._save_slice_info = None
    self._caching_device = None
    self._dtype = dtypes.as_dtype(self._handle.op.get_attr("dtype"))
    self._constraint = None


class UninitializedVariable(BaseResourceVariable):
  """A variable with no initializer."""

  def __init__(  # pylint: disable=super-init-not-called
      self,
      trainable=None,
      caching_device=None,
      name=None,
      shape=None,
      dtype=None,
      constraint=None,
      synchronization=None,
      aggregation=None,
      extra_handle_data=None,
      distribute_strategy=None,
      **unused_kwargs):
    """Creates the variable handle.

    Args:
      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.
      shape: The variable's shape.
      dtype: The variable's dtype.
      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.
      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`.
      extra_handle_data: Optional, another resource handle or Tensor with handle
        data to merge with `shape` and `dtype`.
      distribute_strategy: The tf.distribute.Strategy this variable is being
        created inside of.
    """
    with ops.init_scope():
      self._in_graph_mode = not context.executing_eagerly()
    with ops.init_scope():
      with ops.name_scope(name, "Variable", skip_on_eager=False) as name:
        handle_name = ops.name_from_scope_name(name)
        if self._in_graph_mode:
          shared_name = handle_name
          unique_id = shared_name
        else:
          unique_id = "%s_%d" % (handle_name, ops.uid())
          shared_name = None  # Never shared
        handle = _variable_handle_from_shape_and_dtype(
            shape=shape,
            dtype=dtype,
            shared_name=shared_name,
            name=name,
            graph_mode=self._in_graph_mode,
            initial_value=extra_handle_data)
        if not context.executing_eagerly():
          with ops.name_scope("Read"):
            # Manually assign reads to the handle's device to avoid log
            # messages.
            with ops.device(handle.device):
              value = gen_resource_variable_ops.read_variable_op(handle, dtype)
              _maybe_set_handle_data(dtype, handle, value)
            graph_element = value
          ops.add_to_collection(ops.GraphKeys.GLOBAL_VARIABLES, self)
          # Do *not* add to TRAINABLE_VARIABLES here, even if self._trainable,
          # because retraining or frozen use of imported SavedModels is
          # controlled at higher levels of model building.
        else:
          graph_element = None
    super(UninitializedVariable, self).__init__(
        distribute_strategy=distribute_strategy,
        shape=shape,
        dtype=dtype,
        unique_id=unique_id,
        handle_name=handle_name,
        constraint=constraint,
        handle=handle,
        graph_element=graph_element,
        trainable=trainable,
        synchronization=synchronization,
        aggregation=aggregation)


_pywrap_utils.RegisterType("ResourceVariable", ResourceVariable)
math_ops._resource_variable_type = ResourceVariable  # pylint: disable=protected-access


def _dense_var_to_tensor(var, dtype=None, name=None, as_ref=False):
  return var._dense_var_to_tensor(dtype=dtype, name=name, as_ref=as_ref)  # pylint: disable=protected-access


# Register a conversion function which reads the value of the variable,
# allowing instances of the class to be used as tensors.
ops.register_tensor_conversion_function(BaseResourceVariable,
                                        _dense_var_to_tensor)


class _UnreadVariable(BaseResourceVariable):
  """Represents a future for a read of a variable.

  Pretends to be the tensor if anyone looks.
  """

  def __init__(self, handle, dtype, shape, in_graph_mode, deleter, parent_op,
               unique_id):
    if isinstance(handle, ops.EagerTensor):
      handle_name = ""
    else:
      handle_name = handle.name
    # Only create a graph_element if we're in session.run-land as only
    # session.run requires a preexisting tensor to evaluate. Otherwise we can
    # avoid accidentally reading the variable.
    if context.executing_eagerly() or ops.inside_function():
      graph_element = None
    else:
      with ops.control_dependencies([parent_op]):
        graph_element = gen_resource_variable_ops.read_variable_op(
            handle, dtype)
        _maybe_set_handle_data(dtype, handle, graph_element)
    super(_UnreadVariable, self).__init__(
        handle=handle,
        shape=shape,
        handle_name=handle_name,
        unique_id=unique_id,
        dtype=dtype,
        handle_deleter=deleter,
        graph_element=graph_element)
    self._parent_op = parent_op

  @property
  def name(self):
    if self._in_graph_mode:
      return self._parent_op.name
    else:
      return "UnreadVariable"

  def value(self):
    return self._read_variable_op()

  def read_value(self):
    return self._read_variable_op()

  def _read_variable_op(self):
    with ops.control_dependencies([self._parent_op]):
      result = gen_resource_variable_ops.read_variable_op(
          self._handle, self._dtype)
      _maybe_set_handle_data(self._dtype, self._handle, result)
      return result

  def assign_sub(self, delta, use_locking=None, name=None, read_value=True):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).assign_sub(delta, use_locking, name,
                                                     read_value)

  def assign_add(self, delta, use_locking=None, name=None, read_value=True):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).assign_add(delta, use_locking, name,
                                                     read_value)

  def assign(self, value, use_locking=None, name=None, read_value=True):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).assign(value, use_locking, name,
                                                 read_value)

  def scatter_sub(self, sparse_delta, use_locking=False, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).scatter_sub(sparse_delta, use_locking,
                                                      name)

  def scatter_add(self, sparse_delta, use_locking=False, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).scatter_add(sparse_delta, use_locking,
                                                      name)

  def scatter_max(self, sparse_delta, use_locking=False, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).scatter_max(sparse_delta, use_locking,
                                                      name)

  def scatter_min(self, sparse_delta, use_locking=False, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).scatter_min(sparse_delta, use_locking,
                                                      name)

  def scatter_mul(self, sparse_delta, use_locking=False, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).scatter_mul(sparse_delta, use_locking,
                                                      name)

  def scatter_div(self, sparse_delta, use_locking=False, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).scatter_div(sparse_delta, use_locking,
                                                      name)

  def scatter_update(self, sparse_delta, use_locking=False, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable,
                   self).scatter_update(sparse_delta, use_locking, name)

  def batch_scatter_update(self, sparse_delta, use_locking=False, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable,
                   self).batch_scatter_update(sparse_delta, use_locking, name)

  def scatter_nd_sub(self, indices, updates, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).scatter_nd_sub(indices, updates, name)

  def scatter_nd_add(self, indices, updates, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).scatter_nd_add(indices, updates, name)

  def scatter_nd_update(self, indices, updates, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable,
                   self).scatter_nd_update(indices, updates, name)

  def scatter_nd_max(self, indices, updates, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).scatter_nd_max(indices, updates, name)

  def scatter_nd_min(self, indices, updates, name=None):
    with ops.control_dependencies([self._parent_op]):
      return super(_UnreadVariable, self).scatter_nd_min(indices, updates, name)

  @property
  def op(self):
    """The op for this variable."""
    return self._parent_op


@ops.RegisterGradient("ReadVariableOp")
def _ReadGrad(_, grad):
  """Gradient for read op."""
  return grad


def variable_shape(handle, out_type=dtypes.int32):
  if getattr(handle, "_handle_data",
             None) is None or not handle._handle_data.is_set:  # pylint: disable=protected-access
    return gen_resource_variable_ops.variable_shape(handle, out_type=out_type)
  shape_proto = handle._handle_data.shape_and_type[0].shape  # pylint: disable=protected-access
  if shape_proto.unknown_rank or any(x.size == -1 for x in shape_proto.dim):
    return gen_resource_variable_ops.variable_shape(handle, out_type=out_type)
  return constant_op.constant([x.size for x in shape_proto.dim], dtype=out_type)


@ops.RegisterGradient("ResourceGather")
def _GatherGrad(op, grad):
  """Gradient for gather op."""
  # Build appropriately shaped IndexedSlices
  handle = op.inputs[0]
  indices = op.inputs[1]
  params_shape = variable_shape(handle)
  size = array_ops.expand_dims(array_ops.size(indices), 0)
  values_shape = array_ops.concat([size, params_shape[1:]], 0)
  values = array_ops.reshape(grad, values_shape)
  indices = array_ops.reshape(indices, size)
  return (ops.IndexedSlices(values, indices, params_shape), None)


def _to_proto_fn(v, export_scope=None):
  """Converts Variable and ResourceVariable to VariableDef for collections."""
  return v.to_proto(export_scope=export_scope)


def _from_proto_fn(v, import_scope=None):
  """Creates Variable or ResourceVariable from VariableDef as needed."""
  if v.is_resource:
    return ResourceVariable.from_proto(v, import_scope=import_scope)
  return variables.Variable.from_proto(v, import_scope=import_scope)


ops.register_proto_function(
    ops.GraphKeys.GLOBAL_VARIABLES,
    proto_type=variable_pb2.VariableDef,
    to_proto=_to_proto_fn,
    from_proto=_from_proto_fn)
ops.register_proto_function(
    ops.GraphKeys.TRAINABLE_VARIABLES,
    proto_type=variable_pb2.VariableDef,
    to_proto=_to_proto_fn,
    from_proto=_from_proto_fn)
ops.register_proto_function(
    ops.GraphKeys.MOVING_AVERAGE_VARIABLES,
    proto_type=variable_pb2.VariableDef,
    to_proto=_to_proto_fn,
    from_proto=_from_proto_fn)
ops.register_proto_function(
    ops.GraphKeys.LOCAL_VARIABLES,
    proto_type=variable_pb2.VariableDef,
    to_proto=_to_proto_fn,
    from_proto=_from_proto_fn)
ops.register_proto_function(
    ops.GraphKeys.MODEL_VARIABLES,
    proto_type=variable_pb2.VariableDef,
    to_proto=_to_proto_fn,
    from_proto=_from_proto_fn)
ops.register_proto_function(
    ops.GraphKeys.GLOBAL_STEP,
    proto_type=variable_pb2.VariableDef,
    to_proto=_to_proto_fn,
    from_proto=_from_proto_fn)
ops.register_proto_function(
    ops.GraphKeys.METRIC_VARIABLES,
    proto_type=variable_pb2.VariableDef,
    to_proto=_to_proto_fn,
    from_proto=_from_proto_fn)


@tf_export("__internal__.ops.is_resource_variable", v1=[])
def is_resource_variable(var):
  """"Returns True if `var` is to be considered a ResourceVariable."""
  return isinstance(var, BaseResourceVariable) or hasattr(
      var, "_should_act_as_resource_variable")


def copy_to_graph_uninitialized(var):
  """Copies an existing variable to a new graph, with no initializer."""
  # Like ResourceVariable.__deepcopy__, but does not set an initializer on the
  # new variable.
  # pylint: disable=protected-access
  new_variable = UninitializedVariable(
      trainable=var.trainable,
      constraint=var._constraint,
      shape=var.shape,
      dtype=var.dtype,
      name=var._shared_name,
      synchronization=var.synchronization,
      aggregation=var.aggregation,
      extra_handle_data=var.handle)
  new_variable._maybe_initialize_trackable()
  # pylint: enable=protected-access
  return new_variable


ops.NotDifferentiable("Assert")
ops.NotDifferentiable("VarIsInitializedOp")
ops.NotDifferentiable("VariableShape")


class VariableSpec(tensor_spec.DenseSpec):
  """Describes a tf.Variable."""

  __slots__ = []

  value_type = property(lambda self: BaseResourceVariable)

  def _to_components(self, value):
    raise NotImplementedError

  def _from_components(self, components):
    raise NotImplementedError

  def _from_compatible_tensor_list(self, tensor_list):
    assert len(tensor_list) == 1
    return tensor_list[0]


_pywrap_utils.RegisterType("VariableSpec", VariableSpec)