打开终端 vim ~/.bash_profile
写入python的外部环境变量（本人的版本是3.8） export PATH=${PATH}:/Library/Frameworks/Python.framework/Versions/3.8/bin
在/usr/local/bin/python3.8路径下可查看具体的python安装路径
重命名python alias python="/Library/Frameworks/Python.framework/Versions/3.8/bin/python3.8" (这步很重要，直接关系到默认启动的python版本是否修改）
source ~/.bash_profile
在终端调用python，查看是否修改成功
lilianhong@lilianhongdeMacBook-Pro ~ % python Python 3.8.6 (v3.8.6:db455296be, Sep 23 2020, 13:31:39) [Clang 6.0 (clang-600.0.57)] on darwin Type "help", "copyright", "credits" or "license" for more information.