import time
from time import sleep
from machine import Pin

led1=Pin(0,Pin.OUT)
led2=Pin(1,Pin.OUT)
led3=Pin(2,Pin.OUT)
led4=Pin(3,Pin.OUT)

while True:
    led1.on()
    sleep(0.5)
    led1.off()
    led2.on()
    sleep(0.5)
    led2.off()
    led3.on()
    sleep(0.5)
    led3.off()
    led4.on()
    sleep(0.5)
    led4.off()
    sleep(0.5)