code: def photo_url(self):
          
          if self.url is not None:
              if self.soup is not None:
                  img = self.soup.find('img', class_='Avatar Avatar--l')['src']
                  return img.replace('_l', '_r')
              else:
                  assert (self.card is not None)
                  return PROTOCOL + self.card.img['src'].replace('_xs', '_r')
          else:
              return 'http://pic1.zhimg.com/da8e974dc_r.jpg'
docs: 获取用户头像图片地址.
  
          :return: 用户头像url
          :rtype: str