https://blog.wongcw.com/2019/10/14/python-%e8%84%9a%e6%9c%ac-bug-%e6%88%96%e5%af%bc%e8%87%b4%e4%b8%8a%e7%99%be%e7%af%87%e8%ae%ba%e6%96%87%e5%87%ba%e9%94%99/