python使用环境的设置

virtualenv usage

mkidr ~/pyenv	
cd ~/pyenv
virtualenv pycaffe	#it will setup a new python environtment named pycafffe 
.  pycaffe/bin/activate	#it will activate your pycaffe dependent virtual environment( pycaffe in your shell )
deactiver    #leave your current python environment

//then every package installed by python will be stored independently.
Reference:
http://stackoverflow.com/questions/18966564/pip-freeze-vs-pip-list
https://virtualenvwrapper.readthedocs.io/en/latest/

pip更新软件包的源

mkdir ~/.pip
cd .pip   
vim pip.conf

and add flowing source address

[global]
index-url = https://mirrors.ustc.edu.cn/pypi/web/simple/

当然也可以尝试aliyun的源
注：有时需要更新pip

pip -verbose install  -U pip

系统python不是python2.7

如果系统是python 2.7，那么我们每个virtual python也是python 2.7
但如果系统本身不是我所需要用的python2.7，那么我们需要在本地也安装python 2.7，并且本地安装virtualenv使用我们本地安装的python 2.7
具体安装方法

cs4版本python安装

How to change python from UCS2 to UCS4
解决undefined reference to "PyUnicodeUCS4_*

mac版pyenv安装

安装pyenv

brew install pyenv

查看有哪些版本python可以安装

pyenv install --list

安装

pyenv install 2.7.12

查看当前安装了哪些版

pyenv versions

切换python版本

pyenv global 2.7.12