官方安装指南
https://github.com/yyuu/pyenv#homebrew-on-mac-os-x
注意：
Rebuild the shim binaries. You should do this any time you install a new Python binary. (Examples: installing a new Python version, or installing a package that provides a binary.)
https://www.youtube.com/watch?v=Lw-irZyZmcc
看完视频可以参考教程
http://seisman.info/python-pyenv.html
视频后半部分是设置virtual environment，可以参考如下教程后面的指南设置，此时我的电脑尚没有设置
http://amaral-lab.org/resources/guides/pyenv-tutorial
pyenv version #显示当前使用的Python
pyenv which python #显示当前Python的安裝路径
pyenv global <version> #设置默认的Python版本
pyenv local <version> #在当前路径创建一个.python-version，以后进入这个目录自动切换为该版本
pyenv shell <version> #在当前shell的session中启用某个Python版本，优先级高于global,local
下面这个网页也有一些语句的说明
http://v2in.com/pyenv-installation-and-usage.html
计划以后补装python3
http://stackoverflow.com/questions/30492623/using-both-python-2-x-and-python-3-x-in-ipython-notebook
上面提到了如何装，但是不详细
这里有更多详细如何用notebook的指南
http://jupyter.cs.brynmawr.edu/hub/dblank/public/Jupyter%20Help.ipynb#1.4.2-Enable-Python-3-kernel
http://stackoverflow.com/questions/28831854/how-do-i-add-python3-kernel-to-jupyter-ipython
https://github.com/jupyter/jupyter/issues/52
http://www.motleytech.net/en/2015/11/08/jupyter-python-27-and-35/
搜索关键词
ipython notebook has both python 2 and 3
ipython加入其他kernel官方指南
https://github.com/ipython/ipython/wiki/IPython-kernels-for-other-languages
官方指南kernel for both python 2 and 3
https://ipython.readthedocs.org/en/latest/install/kernel_install.html