code: def iter_tag_users(self, tag_id, first_user_id=None):
          
          while True:
              follower_data = self.get_tag_users(tag_id, first_user_id)
              if 'data' not in follower_data:
                  return
              for openid in follower_data['data']['openid']:
                  yield openid
              first_user_id = follower_data.get('next_openid')
              if not first_user_id:
                  return
docs: 获取标签下粉丝openid列表
  
          :return: 返回一个迭代器，可以用for进行循环，得到openid
  
          使用示例::
  
              from wechatpy import WeChatClient
  
              client = WeChatClient('appid', 'secret')
              for openid in client.tag.iter_tag_users(0):
                  print(openid)