> `shutil.which` could be a direction, but still not enough since it’d break `flit install --python=py` because that’s give you the location of py.exe, not the actual interperter.

This would be fine if you still run the process to get its sys.executable.

Your specific example would never have worked, FWIW, as it always would have picked up pythonA rather than the application one or the base one, unless you were relying on python3/python3.7 not being available on Windows (which is no longer true - they are included in the Store package now).