class_docstr: Stores the mapping between callee and caller methods for a router.
  
  This class is primarily used in a ``get_metadata_routing()`` of a router
  object when defining the mapping between a sub-object (a sub-estimator or a
  scorer) to the router's methods. It stores a collection of ``Route``
  namedtuples.
  
  Iterating through an instance of this class will yield named
  ``MethodPair(callee, caller)`` tuples.
  
  .. versionadded:: 1.3
code: def __repr__(self):
      return str(self._serialize())
  
imports: import inspect
  from collections import namedtuple
  from copy import deepcopy
  from typing import Optional, Union
  from warnings import warn
  from ..None import get_config
  from ..exceptions import UnsetMetadataPassedError
  from ._bunch import Bunch
label_desc: Use image node_id 6 for calling the MethodMapping obj's underlying member method code with example usage: obj.__repr__() and returns: str