class MainWindow(GtkWindow):
    def __init__(self):
        Gtk.Window.__init__(self)
        self.builder = GtkBuilder()
        self.builder.add_from(path_to_my_glade_file)
        self.window = self.builder.get_object('main_window')
        self.window.connect('delete-event', Gtk.main_quit)
        self.window.fullscreen()
        self.window.show_all()

def open_window():
    win = MainWindow()
    win.connect("destroy", Gtk.main_quit)
    Gtk.main()