how to install python3 in ubuntu 18.04 code example

Example: how to install python 3.9 on ubuntu 18.04

Install the dependencies files to build Python. ...
Download the latest Python stable source code. ...
Extract the Python 3.9. ...
Run the configure script. ...
Build the Python 3.9.1. ...
Install the Python 3.9.1. ...
Verify the Python 3.9