Python compatibility

Automax supports Python 3.9 and newer. The GitHub Actions matrix keeps Python 3.9 in the required test set so runtime compatibility regressions are caught before merge.

Why there is an explicit guard

Some Python 3.10+ constructs still parse on Python 3.9 when they appear in runtime expressions, but fail when executed. The common example is this pattern:

isinstance(value, int | float)

That expression raises a TypeError on Python 3.9. The compatible form is:

isinstance(value, (int, float))

Local check

Run the compatibility guard with:

python scripts/check-python39-compat.py

The check scans src/, tests/ and scripts/ for unsafe runtime union usage in isinstance() and issubclass() calls.

CI behavior

The CI workflow runs both:

python -m compileall -q src tests scripts
python scripts/check-python39-compat.py
python -m pytest -q

The explicit guard complements, but does not replace, the Python 3.9 CI matrix.