Test the next Python

To evolve and remain relevant, incompatible changes must happen in Python. The problem is how to migrate existing code to the “next” Python with these incompatible changes.

Deprecation warnings

DeprecationWarning and PendingDeprecationWarning warnings are hidden by default, to not bother users. Developers can use -Wd (-Wdefault) command line option on Python which displays these warnings.

Python Development Mode.

What’s New in Python 3.9: You should check for DeprecationWarning in your code section.

Fedora COPR

Test Rawhide (future Fedora 33) with Python 3.9 as the “system Python”: https://copr.fedorainfracloud.org/coprs/g/python/python3.9/

Projects having “Python nightly in their CI




Searching deprecated API usage


GitHub code search is not powerful enough and there is a lot of noise. (e.g. many people copy CPython source code). On the other hand, Sourcegraph only searches from major repositories, and has powerful filtering. Example: search PyEval_ReleaseLock.

Top 4000 packages

You can download a list of top 4000 PyPI packages in JSON format from hugovk site.

INADA-san’s script to download sdist packages from the JSON file: download_sdist.py.

Note that this script doesn’t download packages without sdist (e.g. only universal wheel). It is because INADA-san has searched Python/C API. The pain of the removal can be reduced by fixing most of top 4000 packages.

Docker images

Barry Warsaw maintains CI Images for Python. Example: .gitlab-ci.yml of flufl.lock.