code: def get_media_requests(self, item, info):
          
          key_generator = item.get(self.QINIU_KEY_GENERATOR_FIELD)
          return [Request(x, meta={'qiniu_key_generator': key_generator}) for x in item.get(self.FILES_URLS_FIELD, [])]
docs: 根据item中的信息, 构造出需要下载的静态资源的Request对象
  
          :param item:
          :param info:
          :return: