class_docstr: Map using ModeKeys as keys.
  
  This class creates an immutable mapping from modes to values. For example,
  SavedModel export of Keras and Estimator models use this to map modes to their
  corresponding MetaGraph tags/SignatureDef keys.
  
  Since this class uses modes, rather than strings, as keys, both "predict"
  (Keras's PREDICT ModeKey) and "infer" (Estimator's PREDICT ModeKey) map to the
  same value.
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code: def __iter__(self):
      return iter(self._keys)
  
file_path: tensorflow/tensorflow/python/keras/saving/utils_v1/mode_keys.py
imports: import collections
label_desc: Use image node_id 4 for calling the ModeKeyMap obj's underlying member method code with example usage: obj.__iter__() and returns: iter