from machine import Pin
import time
red =Pin(0,Pin.OUT)
green =Pin(1,Pin.OUT)
yellow =Pin(2,Pin.OUT)
while True:
 red.value(1)
 green.value(0)
 yellow.value(0)
 time.sleep(1)
 red.value(0)
 green.value(1)
 yellow.value(0)
 time.sleep(1)
 red.value(0)
 green.value(0)
 yellow.value(1)
 time.sleep(1)