code: def validate_destinations(destinations):
      """Validates the `destination` is one of expected types."""
      if not isinstance(
          destinations,
          (
              value_lib.DistributedValues,
              resource_variable_ops.BaseResourceVariable,
              ops.Tensor,
              value_lib.AggregatingVariable,
              six.string_types,
              value_lib.TPUMirroredVariable,
              # LogicalDeviceSpec is only used internally, e.g. as a
              # broadcast destination, never supplied by a user.
              value_lib.LogicalDeviceSpec,
          ),
      ):
          raise ValueError(
              "destinations must be one of a `DistributedValues` object,"
              " a tf.Variable object, or a device string."
          )
  
      if not check_destinations(destinations):
          raise ValueError("destinations can not be empty")
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  import collections
  import enum
  import six
  from tensorflow.python.client import device_lib
  from tensorflow.python.distribute import cross_device_utils
  from tensorflow.python.distribute import device_util
  from tensorflow.python.distribute import reduce_util
  from tensorflow.python.distribute import values
  from tensorflow.python.eager import context
  from tensorflow.python.framework import kernels
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import tensor_util
  from tensorflow.python.ops import array_ops
  from tensorflow.python.ops import math_ops
  from tensorflow.python.ops import resource_variable_ops
  from tensorflow.python.platform import tf_logging
  from tensorflow.python.util.tf_export import tf_export
  from tensorflow.tools.docs import doc_controls
  import tensorflow
  from tensorflow.python.distribute.cross_device_ops import CollectiveAllReduce
  import tensorflow.python.distribute.cross_device_ops
  from byteps.tensorflow.ops import broadcast, _push_pull
  from byteps.tensorflow import local_rank, size
label_desc: Use image node_id 2 for calling a global function with example usage: validate_destinations(destinations) without return types