code: def fetch(self):
          
          LOGGER.debug('Fetching session data: %s', self.id)
          result = yield gen.Task(RedisSession._redis_client.get, self._key)
          if result:
              self.loads(result)
              raise gen.Return(True)
          else:
              raise gen.Return(False)
docs: Fetch the data for the model from Redis and assign the values.
  
          :param method callback: The callback method to invoke when done