from machine import Pin
import time 
from time import sleep

led1=Pin(18,Pin.OUT)
led2=Pin(19,Pin.OUT)
led3=Pin(20,Pin.OUT)
led4=Pin(21,Pin.OUT)
leds=[led1,led2,led3,led4]

while True:
    for l in leds:
        sleep(0.2)
        l.on()
        sleep(0.2)
        l.off()
    print("4 leds blink with time delay of 600ms")