from gi.repository import Gtk

import sys

class MyWindow(Gtk.ApplicationWindow):

    def __init__(self, app):

        Gtk.Window.__init__(self, title="MenuBar Example", application=app)

        self.set_default_size(200, 200)

class MyApplication(Gtk.Application):

    def __init__(self):

        Gtk.Application.__init__(self)

    def do_activate(self):

        win = MyWindow(self)

        win.show_all()

    def do_startup(self):

        Gtk.Application.do_startup(self)

        # a builder to add the UI designed with Glade to the grid:

        builder = Gtk.Builder()

        # get the file (if it is there)

        try:

            builder.add_from_file("menubar_basis.ui")

        except:

            print("file not found")

            sys.exit()

        # we use the method Gtk.Application.set_menubar(menubar) to add the menubar

        # to the application (Note: NOT the window!)

        self.set_menubar(builder.get_object("menubar"))

app = MyApplication()

exit_status = app.run(sys.argv)

sys.exit(exit_status)