Returns an address by input index, a value that matches the list index of the provided
        lookup value, not necessarily the result.

        :param key: an input_index matching the index of the provided address
        :return: a matching Address

def get_index(self, key):
        """
        Returns an address by input index, a value that matches the list index of the provided
        lookup value, not necessarily the result.

        :param key: an input_index matching the index of the provided address
        :return: a matching Address
        """
        try:
            return self[self.index_lookup.get(key)]

        except TypeError:
            raise KeyError