How to use the pymemcache.exceptions.MemcacheError function in pymemcache

if current_time - ldc > self.dead_timeout:
                for server, dead_time in self._dead_clients.items():
                    if current_time - dead_time > self.dead_timeout:
                        logger.debug(
                            'bringing server back into rotation %s',
                            server
                        )
                        self.add_server(*server)
                        self._last_dead_check_time = current_time

        server = self.hasher.get_node(key)
        # We've ran out of servers to try
        if server is None:
            if self.ignore_exc is True:
                return
            raise MemcacheError('All servers seem to be down right now')

        client = self.clients[server]
        return client