mac使用不同python版本

Mac系統自帶的python環境在：

/System/Library/Frameworks/Python.framework/Versions/2.7/      

使用者安裝的python環境預設在：

/Library/Frameworks/Python.framework/Versions/3.7      

python3
Python 3.7.2 (v3.7.2:9a3ffc0492, Dec 24 2018, 02:44:43)
[Clang 6.0 (clang-600.0.57)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>