from machine import Pin
from time import sleep

led_red = Pin(1, Pin.OUT)
led_yellow = Pin(5, Pin.OUT)
led_green = Pin(9, Pin.OUT)

while True:
    led_red.on();
    sleep(20);
    led_red.off();
    led_green.on()
    sleep(10);
    led_green.off();
    led_yellow.on();
    sleep(3);
    led_yellow.off();