class Pin:
    def __init__(self, index):
        self.index = index

class PWM:
    def __init__(self, pin, freq, duty):
        self.pin = pin
        self.freq = freq
        self._duty = duty

    def duty(self, duty):
        self._duty = duty
        print("Pin %d duty %d" % (self.pin.index, self._duty))