code: def retry_task(self):
      
      self.response.set_status(httplib.SERVICE_UNAVAILABLE, "Retry task")
      self.response.clear()
docs: Ask taskqueue to retry this task.
  
      Even though raising an exception can cause a task retry, it
      will flood logs with highly visible ERROR logs. Handlers should uses
      this method to perform controlled task retries. Only raise exceptions
      for those deserve ERROR log entries.