from gi.repository import Gtk

import sys

class MyWindow(Gtk.ApplicationWindow):

    # a window

    def __init__(self, app):

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

        self.set_default_size(250, 50)

        # a button

        button = Gtk.Button()

        # with a label

        button.set_label("Click me")

        # connect the signal "clicked" emitted by the button

        # to the callback function do_clicked

        button.connect("clicked", self.do_clicked)

        # add the button to the window

        self.add(button)

    # callback function connected to the signal "clicked" of the button

    def do_clicked(self, button):

        print("You clicked me!")

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)