mac Python 2.7 升級到3.6.5
下載pkg版本，並安裝。安裝選預設路徑，會安裝到/Library/Frameworks/Python.framework/Versions/目錄下
刪除python2.7
sudo rm -R /System/Library/Frameworks/Python.framework/Versions/2.7
. 移動python3.6
將python3.6安裝到/System/Library/Frameworks/Python.framework/Versions/目錄下：
sudo mv /Library/Frameworks/Python.framework/Versions/3.6 /System/Library/Frameworks/Python.framework/Versions
修改檔案所屬的Group
設定Group為wheel，原來系統自帶的就是這樣的。
sudo chown -R root:wheel /System/Library/Frameworks/Python.framework/Versions/3.6
更新一下Current的Link
在Versions的目錄裡有一個Current的link，是指向當前的Python版本，原始是指向系統自帶的Python2.7，我們把它刪除後，link就失效了，所以需要重新鏈一下
sudo rm /System/Library/Frameworks/Python.framework/Versions/Current
sudo ln -s /System/Library/Frameworks/Python.framework/Versions/3.6 /System/Library/Frameworks/Python.framework/Versions/Current
重新連結可執行檔案
1)先把系統原來的執行檔案刪掉
(sudo rm /usr/bin/pydoc
sudo rm /usr/bin/python
sudo rm /usr/bin/pythonw
sudo rm /usr/bin/python-config)
sudo rm /usr/local/bin/pydoc
sudo rm /usr/local/bin/python
sudo rm /usr/local/bin/pythonw
sudo rm /usr/local/bin/python-config
建立新的連結
sudo ln -s /System/Library/Frameworks/Python.framework/Versions/3.6/bin/pydoc3.6 /usr/local/bin/pydoc
sudo ln -s /System/Library/Frameworks/Python.framework/Versions/3.6/bin/python3.6 /usr/local/bin/python
sudo ln -s /System/Library/Frameworks/Python.framework/Versions/3.6/bin/pythonw3.6 /usr/local/bin/pythonw
sudo ln -s /System/Library/Frameworks/Python.framework/Versions/3.6/bin/python3.6m-config /usr/local/bin/python-config
更新.bash_profile檔案
預設的bash_profile裡python的bin是指向/Library/Frameworks/Python.framework/Versions/3.6/bin的。要改到/System/目錄下
vim ~/.bash_profile (只要能編輯就行)
插入新的Python路徑
# Setting PATH for Python 3.6
# The orginal version is saved in .bash_profile.pysave
PATH="/System/Library/Frameworks/Python.framework/Versions/3.6/bin:${PATH}"
export PATH
解除安裝pkg安裝的python3.6
這一步不做，在使用pip3命令時還是要出錯的(它預設連線到/Library/目錄下照pip3命令，但是實際上應該到/System/Library/目錄下找)。博主掉這個坑好久。
我用的是CleanApp這個軟體來解除安裝原來pkg安裝的python3.6，安裝進來的兩個軟體都解除安裝。
測試：
>python
Python 3.6.5 (v3.6.5:f59c0932b4, Mar 28 2018, 03:03:55)
[GCC 4.2.1 (Apple Inc. build 5666) (dot 3)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>>