#!/usr/bin/python3
import RPi.GPIO as GPIO
import time

led1 = 21
led2 = 16

def setup():
    GPIO.setmode(GPIO.BCM)
    GPIO.setup(led1, GPIO.OUT)
    GPIO.setup(led2, GPIO.OUT)
    
def led_on(led_pin):
    GPIO.output(led_pin, GPIO.HIGH)

def led_off(led_pin):
    GPIO.output(led_pin, GPIO.LOW)

def get_led_pin(led):
    if led == 1:
        return led1
    elif led == 2:
        return led2
    else:
        raise ValueError("Bad LED: ", led)

def main():
    speed = int(input("Speed in milliseconds? ")) / 1000.0

    led = int(input("Led? "))
    led_pin1 = get_led_pin(led)
    led_pin2 = get_led_pin(3-led)
    
    try:
        setup()
        while True:
            led_on(led_pin1)
            led_off(led_pin2)
            time.sleep(speed)
            led_off(led_pin1)
            led_on(led_pin2)
            time.sleep(speed)
    finally:
        led_off(led1)
        led_off(led2)
        GPIO.cleanup

main()