get_key constructs a key given a key type and a key id.
        Keyword arguments:
        key_type -- the type of key (e.g.: 'friend_request')
        key_id -- the key id (e.g.: '12345')

        returns a string representing the key
        (e.g.: 'friend_request:{12345}')

def get_key(self, key_type, key_id):
        """
        get_key constructs a key given a key type and a key id.
        Keyword arguments:
        key_type -- the type of key (e.g.: 'friend_request')
        key_id -- the key id (e.g.: '12345')

        returns a string representing the key
        (e.g.: 'friend_request:{12345}')
        """
        return "{0}:{1}{2}{3}".format(key_type, self._hash_start, key_id,
                                      self._hash_stop)