GtkNotebook minimal code, for debugging

notebook_drag_minimal.py

#!python
# Tester for reorderable tabs. Sure are a lot of GTK regressions here.
# Script is good for either Python2 or Python3.
#
# Copyright waived: http://creativecommons.org/publicdomain/zero/1.0/
# Andrew Chadwick, 2016-05-19.
#
# GTK 3.20.4 terminates the drag as soon as the pointer goes outside the
# notebook whose tab is being dragged. Reordering of tabs within a
# notebook is still possible. https://github.com/mypaint/mypaint/issues/682
#
# GTK 3.16.3 dumps core when trying to drag a tab into an empty
# notebook. The following is seen when you try:
# Gtk:ERROR:[...]/gtk/gtknotebook.c:3832:gtk_notebook_drag_motion: \
# assertion failed: (priv->cur_page != NULL)

import gi

gi.require_version("Gtk", "3.0")
from gi.repository import Gtk


def _main():

    # Window with a grid of notebooks
    win = Gtk.Window()
    win.set_title("test notebook drag")
    grid = Gtk.Grid()

    # Pack a populated notebook
    nb = Gtk.Notebook()
    nb.set_group_name("test1")
    nb.set_size_request(40, 40)
    nb.set_hexpand(True)
    nb.set_vexpand(True)
    for i in range(3):
        s = (
            "Tab %d\n\n"
            "Try dragging me to the\n"
            "empty notebook below."
        ) % (i,)
        w = Gtk.Label(s)
        w.set_size_request(200, 200)
        nb.append_page(w, Gtk.Label("t%d" % (i,)))
        nb.set_tab_reorderable(w, True)
        nb.set_tab_detachable(w, True)
    grid.attach(nb, 0, 1, 1, 1)

    # Pack an empty notebook too
    nb = Gtk.Notebook()
    nb.set_group_name("test1")
    nb.set_size_request(40, 40)
    nb.set_hexpand(True)
    nb.set_vexpand(True)
    grid.attach(nb, 0, 2, 1, 1)

    # Run it...
    win.add(grid)
    win.connect("destroy", Gtk.main_quit)
    win.show_all()
    Gtk.main()


if __name__ == "__main__":
    _main()

Also demonstrates https://bugzilla.gnome.org/show_bug.cgi?id=756160 nicely.