from machine import Pin, ADC
from time import sleep

led = {
  1: Pin(18, Pin.PULL_UP),
  2: Pin(5, Pin.PULL_UP),
  3: Pin(17, Pin.PULL_UP),
  4: Pin(16, Pin.PULL_UP)
}

while True:
  for i in led:
    led[i].on()
    sleep(0.5)
    led[i].off()