docs: def get_proxy(self):
          """
          获取下一个可用的代理
          :return: proxy_host, proxy_port, proxy_username, proxy_password
          """
          if self.proxy_list is None or len(self.proxy_list) <= 0:
              return None, None, None, None
          self.proxy_index += 1
          self.proxy_index = self.proxy_index % len(self.proxy_list)
          item = self.proxy_list[self.proxy_index]
          if len(item) == 2:
              return item[0], item[1], None, None
          else:
              return item[0], item[1], item[2], item[3]