Ubuntu16.04下切换Python版本
update-alternatives --list python
sudo update-alternatives --config pythonubuntu 本身自带python2和python3，也可以自行安装：
update-alternatives --install /usr/bin/python python /usr/bin/python2.7 1
update-alternatives: using /usr/bin/python2.7 to provide /usr/bin/python (python) in auto mode
update-alternatives --install /usr/bin/python python /usr/bin/python3.5 2
update-alternatives: using /usr/bin/python3.5 to provide /usr/bin/python (python) in auto mode
参考仅做备份
原文：https://blog.csdn.net/cym_lmy/article/details/78315139