from machine import Pin
from time import sleep

leds = [Pin(2, Pin.OUT), Pin(6, Pin.OUT),Pin(8, Pin.OUT),Pin(11, Pin.OUT)]

while True:
    for led in leds:
        led.value(1)
        sleep(0.2)
        led.value(0)
    for led in reversed(leds):
        led.value(1)
        sleep(0.2)
        led.value(0)