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

class MyWindow(Gtk.Window):

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

        self.val = 0

        self.box = Gtk.Box(spacing=6)
        self.add(self.box)

        self.button1 = Gtk.Button(label = 'Hello')
        self.button1.connect('clicked', self.on_button1_clicked)
        self.box.pack_start(self.button1, True, True, 0)

        self.button2 = Gtk.Button(label = 'Goodbye')
        self.button2.connect('clicked', self.on_button2_clicked)
        self.box.pack_start(self.button2, True, True, 0)

        self.pbar = Gtk.ProgressBar()
        self.pbar.set_fraction(0.0)
        self.box.pack_start(self.pbar, True, True, 0)

    def on_button1_clicked(self, widget):
        print('Hello')
        while self.val < 1:
            self.update_pbar(self.pbar)
        print('Goodbye')
        Gtk.main_quit()

    def on_button2_clicked(self, widget):
        print('Goodbye')

    def update_pbar(self, widget):
        self.val += 0.1
        self.pbar.set_fraction(self.val)
        time.sleep(0.5)
        while Gtk.events_pending():
            Gtk.main_iteration()
        
win = MyWindow()
win.connect('delete-event', Gtk.main_quit)
win.show_all()
Gtk.main()