upgrade python 3.8 to 3.9 ubuntu code example
Example 1: update ubuntu to python 3.85
sudo apt-get install python3.8
Example 2: how to upgrade python from 2.7 to 2.9 on ubuntu 14.04
git clone https://github.com/pyenv/pyenv.git ~/.pyenv
git clone https://github.com/pyenv/pyenv-virtualenv.git ~/.pyenv/plugins/pyenv-virtualenv