It appears to me to be happening because gobject-introspection only ships a python file for python3.8 not python3.7 which is the default in focal.
$ python3.7 /usr/bin/g-ir-scanner Traceback (most recent call last): File "/usr/bin/g-ir-scanner", line 99, in <module> from giscanner.scannermain import scanner_main File "/usr/lib/x86_64-linux-gnu/gobject-introspection/giscanner/scannermain.py", line 35, in <module> from giscanner.ast import Include, Namespace File "/usr/lib/x86_64-linux-gnu/gobject-introspection/giscanner/ast.py", line 29, in <module> from .sourcescanner import CTYPE_TYPEDEF, CSYMBOL_TYPE_TYPEDEF File "/usr/lib/x86_64-linux-gnu/gobject-introspection/giscanner/sourcescanner.py", line 33, in <module> from giscanner._giscanner import SourceScanner as CSourceScanner ModuleNotFoundError: No module named 'giscanner._giscanner' $ python3.8 /usr/bin/g-ir-scanner ERROR: Need at least one filename $ ls -alh /usr/bin/python3 lrwxrwxrwx 1 root root 9 Oct 18 10:23 /usr/bin/python3 -> python3.7 ** Also affects: python3-defaults (Ubuntu) Importance: Undecided Status: New -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1861556 Title: g-ir-scanner doesn't work To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/gobject-introspection/+bug/1861556/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs