code: def fail_if_not_in_zset(self, key, member, client=None):
          
          self._fail_if_not_in_zset(keys=[key], args=[member], client=client)
docs: Fails with an error containing the string '<FAIL_IF_NOT_IN_ZSET>' if
          the given ``member`` is not in the ZSET ``key``. This can be used in
          a pipeline to assert that the member is in the ZSET and cancel the
          execution otherwise.