#!/usr/bin/python3

import sys
import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk

class AppWindow(Gtk.ApplicationWindow):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, **kwargs)
        self.set_border_width(25)
        button = Gtk.Button.new_with_mnemonic("_Close")
        button.connect("clicked", self.on_button_clicked)
        button.set_relief(Gtk.ReliefStyle.NORMAL)
        self.add(button)
        self.set_size_request(200, 100)

    def on_button_clicked(self, button):
        self.destroy()

class Application(Gtk.Application):

    def __init__(self, *args, **kwargs):
        super().__init__(*args, application_id="org.example.myapp",
                         **kwargs)
        self.window = None

    def do_activate(self):
        if not self.window:
            self.window = AppWindow(application=self, 
                                    title="Hello World!")
        self.window.show_all()
        self.window.present()

if __name__ == "__main__":
    app = Application()
    app.run(sys.argv)