from gi.repository import Gtk

import sys

class MyWindow(Gtk.ApplicationWindow):

    # constructor for a Gtk.ApplicationWindow

    def __init__(self, app):

        Gtk.Window.__init__(self, title="Welcome to GNOME", application=app)

        self.set_default_size(200, 100)

        # create a label

        label = Gtk.Label()

        # set the text of the label

        label.set_text("Hello GNOME!")

        # add the label to the window

        self.add(label)

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)

app = MyApplication()

exit_status = app.run(sys.argv)

sys.exit(exit_status)