from machine import Pin
from utime import sleep
LEDS = [0,1,2,3]
L = [0,0,0,0]
for i in range(4):
  L[i] = Pin(LEDS[i],Pin.OUT)
while True:
  for i in range(4):
    L[i].value(1)
    sleep(0.5)
    L[i].value(0)