python进阶：闭包

详解闭包和装饰器：https://blog.csdn.net/ljt735029684/article/details/80703649

https://www.cnblogs.com/xiaotie/archive/2011/08/03/2126145.html

https://www.liaoxuefeng.com/wiki/1016959663602400/1017434209254976

这篇文章比较清晰https://foofish.net/python-closure.html