Python runtime.txt to specify the Python runtime version

Question

Question

Is runtime.txt the official Python way to specify the python version to use? I suppose it is not what Python supports out of the box and I believe the version of Python runtime depends on the binary package management of each system (apt, brew, yum), unless explicitly download from https://www.python.org/downloads/.

However, if there is a known mechanism to switch Python version, please advise.

Background

There are several articles, mostly from Heiroku related, about runtime.txt to be specific with which version of Python to run.

• IBM Cloud Docs Python

  You can specify the version of Python to be used by your app by setting python-versionnumber in the runtime.txt file in the root of your application.

• Support reading Python version from runtime.txt file?

Answer 1

Review

Local

To get a list of all installed Python versions available through the launcher, run:

py --list

Get sure that version that you want to use presents here.

Then you can crete a virtual environment with specific version like:

py -3.9 -m venv env/place/you/want/to/save/to

or, with virtualenv:

virtualenv --python=python3.9 env/place/you/want/to/save/to

If you want to specify path to your python:

virtualenv --python=/usr/bin/python3.9 env/place/you/want/to/save/to

Instead 3.9 insert version you need.

https://stackoverflow.com/a/67259741/13363187

Server

You can watch your python version with pip:

env/Scripts/activate
pip -V

and specify runtime version at runtime.txt:

python-3.9.10

that version will be used at server automatically (for example, Heroku server support it).