code: def get(self, agent_id, media_id):
          
          return requests.get(self.get_url(agent_id, media_id))
docs: 获取永久素材
          详情请参考
          https://qydev.weixin.qq.com/wiki/index.php?title=%E8%8E%B7%E5%8F%96%E6%B0%B8%E4%B9%85%E7%B4%A0%E6%9D%90
  
          :param agent_id: 企业应用的id
          :param media_id: 媒体文件 ID
          :return: requests 的 Response 实例