from machine import Pin
from time import sleep

led_red = Pin(12,Pin.OUT)
led_yel = Pin(14,Pin.OUT)
led_gre = Pin(27,Pin.OUT)

leds = [led_red, led_yel, led_gre]
cnt = 0

while True:
    cnt %= 3
    for i in range(0,len(leds)):
        if cnt == i:
            leds[i].value(True)
        else:
            leds[i].value(False)
    cnt+=1
    sleep(0.25)