class OutPutPins:
    def turn_on(self):
        print("turn on\n")

    def turn_off(self):
        print("turn off\n")

class PiFaceDigital:
    output_pins = [0,0]
    def __init__(self):
        self.output_pins[1] = OutPutPins()


if __name__ == '__main__':
    piface = PiFaceDigital()
    piface.output_pins[1].turn_on()