code: def motto(self):
          
          if self.url is None:
              return ''
          else:
              if self.soup is not None:
                  bar = self.soup.find(
                      'div', class_='title-section')
                  if len(bar.contents) < 4:
                      return ''
                  else:
                      return bar.contents[3].text
              else:
                  assert self.card is not None
                  motto = self.card.find('div', class_='tagline')
                  return motto.text if motto is not None else ''
docs: 获取用户自我介绍，由于历史原因，我还是把这个属性叫做motto吧.
  
          :return: 用户自我介绍
          :rtype: str