class_docstr: Allow to request TPU hardware and skip non-TPU combinations.
  
  This class expects test_combinations to be generated with `NamedDistribution`
  wrapping instances of `tf.distribute.Strategy`.
  
  Optionally, the `required_tpus` parameter is supported.  TPU hardware is
  required, if its argument is `True` or > 0.
  
  Optionally, the `use_cloud_tpu` parameter is supported. If TPU hardware is
  required by `required_tpus`, it specifically must be a Cloud TPU (specified
  with `--tpu`) if `use_cloud_tpu` is `True`.
  
  Attributes:
    TPU_TEST: The environment is considered to have TPU hardware available if
              the name of the program contains "test_tpu".
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code: def parameter_modifiers(self):
      return [
          combinations_lib.OptionalParameter("required_tpus"),
          combinations_lib.OptionalParameter("required_tpu"),
          combinations_lib.OptionalParameter("use_cloud_tpu"),
      ]
  
imports: import collections
  import copy
  import re
  import sys
  import types
  import unittest
  from absl import app
  import six
  from tensorflow.python.client import session
  from tensorflow.python.distribute import collective_all_reduce_strategy
  from tensorflow.python.distribute import distribute_lib
  from tensorflow.python.distribute import multi_process_runner
  from tensorflow.python.distribute import multi_worker_test_base
  from tensorflow.python.eager import context
  from tensorflow.python.eager import def_function
  from tensorflow.python.framework import combinations
  from tensorflow.python.framework import config
  from tensorflow.python.framework import ops
  from tensorflow.python.framework import test_combinations
  from tensorflow.python.framework import test_util
  from tensorflow.python.platform import flags
  from tensorflow.python.platform import tf_logging
  from tensorflow.python.util import tf_decorator
  from tensorflow.python.util import tf_inspect
  from tensorflow.python.util.tf_export import tf_export
label_desc: Use image node_id 2 for calling the TPUCombination obj's underlying member method code with example usage: obj.parameter_modifiers() and returns: list