I had a bug that was only showing up in CI against Python 3.8.

I used the following pattern with pyenv to quickly run the tests against that specific version.

(I had previously installed pyenv using brew install pyenv.)

Seeing what versions I had already

pyenv versions

This outputs (on my machine):

  system
  3.7.16
  3.8.17

To see all possible versions:

pyenv install --list

That's a long list! I grepped it for 3.8:

pyenv install --list | grep '3.8'

  3.8.0
  3.8-dev
  3.8.1
  3.8.2
  ...
  3.8.14
  3.8.15
  3.8.16
  3.8.17
  ...

Installing a specific version

I installed 3.8.17 like this:

pyenv install 3.8.17

This took a long time, because it compiled it from scratch.

Using that version via a virtual environment

I decided to use that version of Python directly. The binary was installed here:

~/.pyenv/versions/3.8.17/bin/python

I created a temporary virtual environment in /tmp like this:

~/.pyenv/versions/3.8.17/bin/python -m venv /tmp/py38env

Then installed my current project into that environment like so:

/tmp/py38env/bin/pip install -e '.[test]'

Now I can run the tests like this:

/tmp/py38env/bin/pytest