from machine import Pin
from time import sleep
Red_led = Pin(3,Pin.OUT);
Yellow_led = Pin(4,Pin.OUT);
Green_led = Pin(2,Pin.OUT);
while True:
    Red_led.on()
    Yellow_led.off()
    Green_led.off()
    sleep(1)
    Yellow_led.on()
    Green_led.off()
    Red_led.off()
    sleep(1)
    Green_led.on()
    Red_led.off()
    Yellow_led.off()
    sleep(1)