Small Gtk app that toggles images according to the button state.

gtk_leds1.py

from gi.repository import Gtk


class LedControl(Gtk.Window):
    """
        A simple app that changes images according to the button status.
    """
    def __init__(self):
        Gtk.Window.__init__(self, title="LED Control")
        self.set_border_width(6)
        self.set_default_size(200, 250)

        okno = Gtk.Table(4, 2, True)
        self.add(okno)

        self.leds = []
        for i in range(4):
            button = Gtk.ToggleButton("LED %s" % i)
            button.connect("toggled", self.led_button_handler, str(i))
            button.set_border_width(2)
            img = Gtk.Image()
            img.set_from_file("LED_off.png")
            okno.attach(button, 0, 1, i, i + 1)
            okno.attach(img, 1, 2, i, i + 1)
            self.leds.append(img)

    def led_button_handler(self, button, name):
        self.leds[int(name)].set_from_file(
            "LED_on.png" if button.get_active() else "LED_off.png",
        )

if "__main__" == __name__:
    app = LedControl()
    app.connect("delete-event", Gtk.main_quit)
    app.show_all()
    Gtk.main()