code: def unhelpful(self, answer, unhelpful=True):
          
          from .answer import Answer
          if isinstance(answer, Answer) is False:
              raise ValueError('argument answer need to be Zhihu.Answer object.')
          if answer.author.url == self.url:
                  return False
          data = {
              '_xsrf': answer.xsrf,
              'aid': answer.aid
          }
          res = self._session.post(Unhelpful_Url if unhelpful else Cancel_Unhelpful_Url,
                                   data=data)
          return res.json()['r'] == 0
docs: 没有帮助或取消没有帮助回答
  
          :param Answer answer: 要没有帮助或取消没有帮助回答
          :param unhelpful: True-->没有帮助，False-->取消没有帮助
          :return: 成功返回 True，失败返回 False
          :rtype: bool