which python 查看安装目录
python --version 查看版本号
python 目录/xx文件名 运行xx文件
brew install python3 下载新版python3
python3 --version
python3 -m pip install psycopg2 --user（不加--user会报错：）
You are using pip version 10.0.1, however version 20.0.2 is available.
You should consider upgrading via the 'pip install --upgrade pip' command.
