code: def refresh(self):
          
          super().refresh()
          self._html = None
          self._title = None
          self._details = None
          self._answer_num = None
          self._follower_num = None
          self._topics = None
          self._last_edit_time = None
          self._logs = None
docs: 刷新 Question object 的属性. 
          例如回答数增加了, 先调用 ``refresh()`` 
          再访问 answer_num 属性, 可获得更新后的答案数量.
          
          :return: None