# coding: utf-8
import gi
gi.require_version('Gtk', '3.0')
from gi.repository import Gtk

class MyWindow(Gtk.Window):

    def __init__(self):
        Gtk.Window.__init__(self, title="Hello World")

        self.button = Gtk.Button(label="Click Here")
        self.button.connect("clicked", self.on_button_clicked)
        self.add(self.button)

    def on_button_clicked(self, widget):
        print("Hello World")

win = MyWindow()
win.connect("delete-event", Gtk.main_quit)  # connecting to the window’s delete event to ensure that the application is terminated if we click on the x to close the window.
win.show_all()                              # display the window
Gtk.main()                                  # start the GTK+ processing loop which we quit when the window is closed