code: def find_action_name_by_value(registry, target_action_instance):
      
      target_type = type(target_action_instance)
      for key, value in six.iteritems(registry['action']):
          if value is target_type:
              if key is None:
                  return 'store'
              return key
      return None
docs: the association of a name of an action class with a human readable
      string is exposed externally only at the time of argument definitions.
      This routine, when given a reference to argparse's internal action
      registry and an action, will find that action and return the name under
      which it was registered.