code: def weibo_url(self):
          
          if self.url is None:
              return None
          else:
              tmp = self.soup.find(
                  'a', class_='zm-profile-header-user-weibo')
              return tmp['href'] if tmp is not None else 'unknown'
docs: 获取用户微博链接.
  
          :return: 微博链接地址，如没有则返回 ‘unknown’
          :rtype: str