1.安装Python 3
2.查看Python3 安装路径
打开终端，输入which python3，查看路径 /Library/Frameworks/Python.framework/Versions/3.7/bin/python3
3.打开配置文件
open ~/.bash_profile
4.写入外部环境变量
export PATH=${PATH}:/Library/Frameworks/Python.framework/Versions/3.7/bin/python3
5.重命名Python
alias python="/Library/Frameworks/Python.framework/Versions/3.7/bin/python3"
6.关闭文件
7.终端执行命令：source ~/.bash_profile
8.终端执行命令： python检查Python版本