Return index of *value* in self.

        Raises ValueError if *value* is not found.

def index(self, value):
        """
        Return index of *value* in self.

        Raises ValueError if *value* is not found.
        """
        # pylint: disable=arguments-differ
        for idx, val in enumerate(self):
            if value == val:
                return idx
        raise ValueError('{0!r} is not in dict'.format(value))