How to install older python version on Debian

[Robbi Nespu <robbinespu@gmail.com>]

Dear Debian Python,

I would like to install older python (version 3.6) on my venv environment

$ inxi -S
System:    Host: debian Kernel: 5.10.0-4-amd64 x86_64 bits: 64 Desktop: 
KDE Plasma 5.20.5
           Distro: Debian GNU/Linux bullseye/sid

(venv)$ python --version
Python 3.9.2

on fedora I can easily do something like this[1], but on debian I 
wondering how I can achieve the same thing, as it look like and I guess 
older python are not available directly on repository

$ sudo apt-cache pkgnames python3.
python3.9-venv
python3.9-examples
python3.9-full
python3.9-dbg
python3.9-dev
python3.9-doc
python3.9
python3.9-minimal

If my guest are right. Could you suggest me a solution how to have 
multiple python version so I can load inside venv?

[1] https://robbinespu.gitlab.io/blog/2019/07/23/Python-36-with-VirtualEnv/

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Email : Robbi Nespu <robbinespu AT SPAMFREE gmail DOT com>
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