If for some reason Tom’s suggestion doesn’t work, I looked at the bash script at:
script.module.zap2epg/bin/tv_grab_zap2epg
That’s the script that I’m guessing TVHeadEnd calls, which in turn calls a python script. On line 28 it calls that python script using:
python $ADDON_DIR/zap2epg.py
Change that to:
python3 $ADDON_DIR/zap2epg.py