code: def policy_scope(policy):
      """A context manager that sets the global Policy under it.
  
      Args:
        policy: A Policy, or a string that will be converted to a Policy..
  
      Yields:
        Nothing.
      """
      old_policy = _global_policy
      try:
          set_global_policy(policy)
          yield
      finally:
          set_global_policy(old_policy)
  
imports: import contextlib
  from tensorflow.python.framework import dtypes
  from tensorflow.python.keras import backend
  from tensorflow.python.keras.engine import base_layer_utils
  from tensorflow.python.keras.mixed_precision import device_compatibility_check
  from tensorflow.python.keras.mixed_precision import loss_scale
  from tensorflow.python.keras.utils import generic_utils
  from tensorflow.python.platform import tf_logging
  from tensorflow.python.training.experimental import mixed_precision_global_state
label_desc: Use image node_id 4 for calling a global function with example usage: policy_scope(policy) without return types