Minimum Python version

CVW targets a minimum Python version of 3.9 for compatibility with Debian 11. We’re already using Python features that aren’t compatible with 3.9 in this project. We need to decide on a minimum Python version and update the existing scripts to ensure they work with that version.

This is less of an issue if we decide to proceed with using uv as part of the development flow because it is able to download and run any recent version of Python without needing distro support.