https://yuehualiu.medium.com/python-%E8%BF%B4%E5%9C%88-loop-%E8%AE%93%E4%B8%80%E6%A8%A3%E7%9A%84%E4%BA%8B%E6%83%85%E9%87%8D%E8%A4%87%E5%9F%B7%E8%A1%8C-bfd6c5956278
