Black is the uncompromising Python code formatter. By using it, you
agree to cede control over minutiae of hand-formatting. In return,
Black gives you speed, determinism, and freedom from pycodestyle
nagging about formatting. You will save time and mental energy for
more important matters.

python3-black 22.12.0 is the last available version for Slackware 15.0.
Newer versions require a newer python-packaging.