I can test my python script from the command line.
python index.cgi

In the default a2hosting account, I can run any version of python.
python –version
python3 –version
python3.7 –version

I can also create a virtual environment, in which I can use pip to install packages.
Then I can use this environment to run cgi scripts.

We already have python cgi available, as in index.cgi. But cgi is not an efficient way to run python. So now we will setup a more modern python implementation.
See a2hosting docs here.
How to use the Python Selector in cPanel
Python Articles

In cPanel, Setup Python App, Create Application.

Fill in the form thusly:

• Python version: 3.7.12
• Application root: /home/username/webprod/sandbox/sandbox/html/pvc
• Application URL: sandbox.voyc.com/pvc
• Application startup file: passenger_wsgi.py (default, created automatically)
• Application Entry point: application (default, the name of a function in the startup file)
• Passenger log file: /home/username/logs/user/sandbox.py.log

Evidently this is Phusion Passenger.
From the URL we can call only one python function: the Entry Point in the Startup File.
Page navigation must be handled by the entry point function.
Presumably one could create multiple applications on one subdomain?

The Application Root is similar to DocRoot.
The setup creates this folder and installs the startup file and three folders.
passenger_wsgi.py public/ pycache/ tmp/

This application can be stopped, restarted, and destroyed from the cPanel page.
I sometimes need to do a restart to make my program changes take effect.

The cPanel, Setup Python App, program already created a virtual environment for this app. Its location is /home/username/virtualenv/webprod/sandbox/sandbox/html/pvc/3.7. This folder contains bin/, lib/, and lib64 folders. To activate this enviroment offline. source /home/username/virtualenv/webprod/sandbox/sandbox/html/pvc/3.7

Then I can install packages using Pip, and these packages are available to the web app as well.