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

class App:

    def on_btnUpdate_clicked(self, btn):
            self.label.set_text("Aggiornato!")

    def on_btnQuit_clicked(self, btn):
            Gtk.main_quit()

    def gtk_main_quit(self, btn):
            Gtk.main_quit()

    def __init__(self):
        self.builder = Gtk.Builder()
        self.builder.add_from_file('test.glade')
        self.builder.connect_signals(self)

        self.window = self.builder.get_object("windowMain")
        self.window.show()

        self.label = self.builder.get_object("lblText")

        Gtk.main()

    def __destroy__(self):
        Gtk.main_quit()

if __name__ == '__main__':
    a = App()