Using gtk_container_foreach or [ http://developer.gnome.org/gtk3/3.4/GtkContainer.html#gtk-container-foreach gtk_container_forall] does expect the callback data to be passed in Python, it does work in a subclassed container due to Carlos [http://git.gnome.org/browse/gtk+/commit/?id=db569cbee7e3842d802c5f1d53e28d0dde98ffeb fix in the GtkCallback annotations].