code: def top_i_answers(self, i):
          
          for j, a in enumerate(self.answers):
              if j <= i - 1:
                  yield a
              else:
                  return
docs: 获取排名在前几位的答案.
  
          :param int i: 获取前几个
          :return: 答案对象，返回生成器
          :rtype: Answer.Iterable