python3-setuptools-scm-opt (setuptools-scm installed to /opt)

setuptools_scm extracts Python package versions from git or hg
metadata instead of declaring them as the version argument or in a SCM
managed file.

# Build your package with this version to fix errors like the following:
ImportError: cannot import name '__version__' from ...

NOTE:
Installs to /opt/python3.9/site-packages

Add the following before the python3 build commands in your
Slackbuild to use this version over the stock one in 15.0:

export PYTHONPATH=/opt/python3.9/site-packages/