官方文档：
https://docs.python.org/3/tutorial/index.html
推荐：
https://www.tutorialspoint.com/python3/index.htm
https://www.tutorialspoint.com/python/index.htm
https://www.tutorialspoint.com/python_technologies_tutorials.htm
交互：
视频教学：
https://www.tutorialspoint.com/python_for_beginners_learn_python_programming_python_3/index.asp
https://www.tutorialspoint.com/python-for-beginners-python-3/index.asp
https://www.tutorialspoint.com/practical-python-learn-python-basics-step-by-step-python-3/index.asp
py 2
https://www.pythonforbeginners.com/python-tutorial
