How to use the pymemcache.client.base._check_key function in pymemcache

def _get_client(self, key):
        _check_key(key, self.allow_unicode_keys, self.key_prefix)
        if len(self._dead_clients) > 0:
            current_time = time.time()
            ldc = self._last_dead_check_time
            # we have dead clients and we have reached the
            # timeout retry
            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)