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.
  # ==============================================================================
  """Flags for managing compute devices. Currently only contains TPU flags."""
  
  from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  
  from absl import flags
  import tensorflow as tf
  
  from official.utils.flags._conventions import help_wrap
  
  
  def require_cloud_storage(flag_names):
    """Register a validator to check directory flags.
    Args:
      flag_names: An iterable of strings containing the names of flags to be
        checked.
    """
    msg = "TPU requires GCS path for {}".format(", ".join(flag_names))
    @flags.multi_flags_validator(["tpu"] + flag_names, message=msg)
    def _path_check(flag_values):  # pylint: disable=missing-docstring
      if flag_values["tpu"] is None:
        return True
  
      valid_flags = True
      for key in flag_names:
        if not flag_values[key].startswith("gs://"):
          tf.compat.v1.logging.error("{} must be a GCS path.".format(key))
          valid_flags = False
  
      return valid_flags
  
  
  def define_device(tpu=True):
    """Register device specific flags.
    Args:
      tpu: Create flags to specify TPU operation.
    Returns:
      A list of flags for core.py to marks as key flags.
    """
  
    key_flags = []
  
    if tpu:
      flags.DEFINE_string(
          name="tpu", default=None,
          help=help_wrap(
              "The Cloud TPU to use for training. This should be either the name "
              "used when creating the Cloud TPU, or a "
              "grpc://ip.address.of.tpu:8470 url. Passing `local` will use the"
              "CPU of the local instance instead. (Good for debugging.)"))
      key_flags.append("tpu")
  
      flags.DEFINE_string(
          name="tpu_zone", default=None,
          help=help_wrap(
              "[Optional] GCE zone where the Cloud TPU is located in. If not "
              "specified, we will attempt to automatically detect the GCE "
              "project from metadata."))
  
      flags.DEFINE_string(
          name="tpu_gcp_project", default=None,
          help=help_wrap(
              "[Optional] Project name for the Cloud TPU-enabled project. If not "
              "specified, we will attempt to automatically detect the GCE "
              "project from metadata."))
  
      flags.DEFINE_integer(name="num_tpu_shards", default=8,
                           help=help_wrap("Number of shards (TPU chips)."))
  
    return key_flags
  