Ubuntu16.04默认安装了Python2.7和3.5
系统自带的python千万不能卸载！
输入python
sudo add-apt-repository ppa:jonathonf/python-3.6
完了，按enter键确认
再输入如下
sudo apt-get update
sudo apt-get install python3.6
按Y确认
调整python3的优先级，使得3.6优先级较高
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.5 1
sudo update-alternatives --install /usr/bin/python3 python3 /usr/bin/python3.6 2
更改默认值，python默认为Python2，现在修改为Python3
sudo update-alternatives --install /usr/bin/python python /usr/bin/python2 100
sudo update-alternatives --install /usr/bin/python python /usr/bin/python3 150
sudo su
update-alternatives --config python
https://blog.csdn.net/qq_42693848/article/details/88900553
https://www.cnblogs.com/Yanfang20180701/p/10588087.html
https://blog.csdn.net/qq_33733356/article/details/106969109
evo
https://www.cnblogs.com/rjjhyj/p/11646791.html