On systems without `future`, there would issues with missing `past`.
from past.builtins import xrange
ModuleNotFoundError: No module named 'past'
Installing `future` like `pip install future` can help, but it bothers.
Changing `xrange` to `range` can be OK since python3 has no `xrange`
anymore, while both 2 and 3 can have `range`.
The performance impact with python2 should be minor.
Tested OK on latest Debian bullseye/bookworm, Ubuntu jammy, and
Archlinux, with python2 linked to 2.7.18, or 2.7.3, while python linked
to 3.10.8, 3.10.6, or 3.9.2.
c8fbf13b96