class Gtk::App does Inline::Python::PythonParent['__main__', 'gtk'] { } Fails with: invalid syntax (<string>, line 1) trying to create subclass Gtk::App from __main__.gtk Part of what needs to be done is probably: $subclass_name ~~ s:g{'::'}='__'; # on line 450 Inline/Python.pm6 I'm working on a PR, you'll be notified if I get it working.