code: def _hashable_var_key(var):
      """Returns a hashable key to identify the given Variable."""
  
      # In TF 2, Variables themselves are not hashable, so cannot be dict keys.
      # Error is "Tensor is unhashable if Tensor equality is enabled. Instead, use
      # tensor.experimental_ref() as the key". For a related issue, see:
      # https://github.com/tensorflow/tensorflow/issues/32139
      ref_op = getattr(var, "experimental_ref", None)
      if callable(ref_op):
          return ref_op()
      return var
  
imports: from __future__ import absolute_import
  from __future__ import division
  from __future__ import print_function
  from distutils.version import LooseVersion
  import tensorflow.compat.v1
  import tensorflow.compat.v2
  from tensorflow.python import tf2
  from tensorflow.python.keras.metrics import Metric
  from tensorflow.python.tpu import tpu_function
  from tensorflow_estimator.python.estimator.head import regression_head
label_desc: Use image node_id 6 for calling a global function with example usage: _hashable_var_key(var) and returns: var, ref_op