https://blog.youkuaiyun.com/csdnnews/article/details/88729964
https://github.com/selfteaching/the-craft-of-selfteaching
https://docs.python.org/3/tutorial/index.html
- https://docs.python.org/zh-cn/3/tutorial/index.html (for v.3.7.2)
- http://www.pythondoc.com/pythontutorial3/ (for v.3.6.3)
https://github.com/xiaolai/everyone-can-use-english
python 的???