mac上默认的python版本为2.7.10版本，需要升级到python3 版本，通过brew升级
- $brew install python3
提示错误
$ brew install python3 Warning: python3 3.6.3 is already installed, it's just not linked. You can use `brew link python3` to link this version. $ brew link python3 Linking /usr/local/Cellar/python3/3.6.3... Error: Permission denied @ dir_s_mkdir
发现/usr/local/下没有路径/usr/local/Frameworks
需要新建该路径，并修改权限
解决：
$ sudo mkdir /usr/local/Frameworks $ sudo chown $(whoami):admin /usr/local/Frameworks
成功：
$ brew link python3 Linking /usr/local/Cellar/python3/3.6.3... 1 symlinks created