from machine import Pin
from time import sleep

red = Pin(2, Pin.OUT)
green = Pin(4, Pin.OUT)
yellow = Pin(5, Pin.OUT)
while True:
red.on()
green.off()
yellow.off()
sleep(2)

red.off()
green.on()
yellow.off()
sleep(2)

red.off()
green.off()
yellow.on()
sleep(1)