from gi.repository import Gtk

import sys

class MyApplication(Gtk.Application):

    def do_activate(self):

        # create a Gtk Window belonging to the application itself

        window = Gtk.Window(application=self)

        # set the title

        window.set_title("Welcome to GNOME")

        # show the window

        window.show_all()

# create and run the application, exit with the value returned by

# running the program

app = MyApplication()

exit_status = app.run(sys.argv)

sys.exit(exit_status)