code: def set_key(self, key, value, namespace=None, expire=0):
          
          with (yield from self._pool) as redis:
              if namespace is not None:
                  key = self._get_key(namespace, key)
              yield from redis.set(key, value, expire=expire)
docs: Set a key in a cache.
          :param key: Key name
          :param value: Value
          :param namespace : Namespace to associate the key with
          :param expire: expiration
          :return: