mac 自带 python2
python  --version
Python 2.7.18

下载 python3 

https://registry.npmmirror.com/binary.html?path=python/

python-3.7.8-macosx10.9.pkg

which python3
/usr/local/bin/python3

python3  --version
Python 3.7.8

alias python="/usr/local/bin/python3"
python
Python 3.7.8 (v3.7.8:4b47a5b6ba, Jun 27 2020, 04:47:50) 
[Clang 6.0 (clang-600.0.57)] on darwin

cat ~/.bash_profile

# Setting PATH for Python 3.7
# The original version is saved in .bash_profile.pysave
PATH="/Library/Frameworks/Python.framework/Versions/3.7/bin:${PATH}"
export PATH


python3 -m http.server 8030
Serving HTTP on 0.0.0.0 port 8030 (http://0.0.0.0:8030/) ...



推荐使用 anaconda
Anaconda 是目前国内外高校教学Python最流行的软件平台，包含了Python的环境管理、代码编辑器、包管理等，一键安装方便快捷。


 anaconda 使用