Mac中切换Python版本，Python2和Python3之间的切换
Mac电脑中默认安装的是Python2.7，而有时会提示DEPRECATION: Python 2.7 reached the end of its life on January 1st, 2020. Please upgrade your Python as Python 2.7 is no longer maintained. pip 21.0 will drop support for Python 2.7 in January 2021. More details about Pyth
