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

class PyApp(Gtk.Window):

    def __init__(self):
        super(PyApp, self).__init__()
        self.set_title('Hello World!!')
        self.set_position(Gtk.WindowPosition.CENTER_ALWAYS)
        self.connect('destroy', Gtk.main_quit)
        self.set_size_request(250, 150)
        self.show()


PyApp()
Gtk.main()
