转:http://blog.csdn.net/liuchunming033/article/details/46008301
转:http://www.jb51.net/article/85527.htm
安装指定版本:http://www.cnblogs.com/technologylife/p/6635631.html
mac上安装python3的虚拟环境: virtualenv -p /usr/local/bin/python3 venv3
那个路径是通过which python3找到的