Pin Python version to 3.12

[browniebroke]

Description

Looking at #5450 I noticed that Python 3.13 classifier was added, which promopted me to look at which version of Python was used to run the tests, and it turns out they run using Python 3.13:

• https://github.com/cookiecutter/cookiecutter-django/actions/runs/11285345637/job/31387993157?pr=5450#step:5:8
• https://github.com/cookiecutter/cookiecutter-django/actions/runs/11285345637/job/31387992848?pr=5450#step:5:9

Checklist:

• I've made sure that tests are updated accordingly (especially if adding or updating a template option)
• I've updated the documentation or confirm that my change doesn't require any updates

Rationale

Run tests on the same Python version as we officially support

[browniebroke]

I also noticed that our bare metal tests run on Python 3.10 since we migrated the template to uv: https://github.com/cookiecutter/cookiecutter-django/actions/runs/11194437208/job/31120912239?pr=5356#step:7:609

Previous run was on Python 3.12 (as expected): https://github.com/cookiecutter/cookiecutter-django/actions/runs/11193688349/job/31119292907?pr=5430#step:7:538

[foarsitter]

So the project itself (not the template) is compatible with 3.13?

[browniebroke]

No, the template tests were running on 3.13, we don't run any tests in the project itself on that job, just linters. It seems that the project tests were downgraded to python 3.10 in the bare metal tests.

[foarsitter]

Is this required? Capping python in pyproject.toml should be sufficient was my expectation.

[browniebroke]

It doesn't seem to be respecting it because the generated project is not using uv yet. It's for the test_bare.sh script

[browniebroke]

I'll remove it to confirm

[browniebroke]

The pytest run uses Python 3.10 here platform linux -- Python 3.10.12:

https://github.com/cookiecutter/cookiecutter-django/actions/runs/11306934810/job/31448084312?pr=5456#step:7:561

This is because these lines use the first pip and pytest on the PATH, which are not the one from uv:

cookiecutter-django/tests/test_bare.sh

Line 21 in 822c1c0

pip install -r requirements/local.txt

cookiecutter-django/tests/test_bare.sh

Line 24 in 822c1c0

pytest

[foarsitter]

Ah yes, you are right. The problem is clear to me now.

[browniebroke]

I tried another approach, runing all commands from the script via uv, but that doesn't seem to work. I'll revert back to using actions/setup-python as it seems more straightforward