另：恭喜 Python 2 正式退休。
在 2.7.18 版本以后，Python 2 将正式停止维护。
ref: https://www.python.org/dev/peps/pep-0373/#maintenance-releases
pythonclock.org
Python 2.7 Countdown
Python 2.7 will retire in 2020. Learn more and see the countdown here.