1. 安装Python软件工具
sudo apt-get install python-software-properties
2. 添加仓库镜像源
sudo add-apt-repository ppa:fkrull/deadsnakes
或
sudo vim /etc/apt/sources.list.d/fkrull-ubuntu-deadsnakes-xenial.list
添加源：deb http://ppa.launchpad.net/fkrull/deadsnakes/ubuntu xenial main
3. 更新源
sudo apt-get update
4. 从本地仓库安装python
sudo apt-get install python3.6