text: # Copyright 2018 The TensorFlow Authors. All Rights Reserved.
  #
  # Licensed under the Apache License, Version 2.0 (the "License");
  # you may not use this file except in compliance with the License.
  # You may obtain a copy of the License at
  #
  #     http://www.apache.org/licenses/LICENSE-2.0
  #
  # Unless required by applicable law or agreed to in writing, software
  # distributed under the License is distributed on an "AS IS" BASIS,
  # WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  # See the License for the specific language governing permissions and
  # limitations under the License.
  # ==============================================================================
  """Device-related support functions."""
  
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  from tensorflow.python.eager import context
  from tensorflow.python.framework import device as tf_device
  from tensorflow.python.framework import ops
  
  
  def canonicalize(d):
    d = tf_device.DeviceSpec.from_string(d)
    assert d.device_type is None or d.device_type == d.device_type.upper(), (
        "Device type '%s' must be all-caps." % (d.device_type,))
    # Fill in missing device fields using defaults.
    result = tf_device.DeviceSpec(
        job="localhost", replica=0, task=0, device_type="CPU", device_index=0)
    result.merge_from(d)
    return result.to_string()
  
  
  class _FakeNodeDef(object):
    """A fake NodeDef for _FakeOperation."""
  
    def __init__(self):
      self.op = ""
      self.name = ""
  
  
  class _FakeOperation(object):
    """A fake Operation object to pass to device functions."""
  
    def __init__(self):
      self.device = ""
      self.type = ""
      self.name = ""
      self.node_def = _FakeNodeDef()
  
    def _set_device(self, device):
      self.device = ops._device_string(device)  # pylint: disable=protected-access
  
  
  def current():
    """Return a string (not canonicalized) for the current device."""
    # TODO (josh11b): Work out how this function interacts with ops.colocate_with. id:3467
    # https://github.com/imdone/tensorflow/issues/3466
    ctx = context.context()
    if ctx.executing_eagerly():
      d = ctx.device_name
    else:
      op = _FakeOperation()
      ops.get_default_graph()._apply_device_functions(op)  # pylint: disable=protected-access
      d = op.device
    return d
  