from machine import Pin
from time import sleep

while True:
    for i in range(2, 11, 2):
        led = Pin(i, Pin.OUT)
        led.value(1)
        sleep(0.3)
        led.value(0)
    for i in range(9,0,-2):
        led = Pin(i, Pin.OUT)
        led.value(1)
        sleep(0.3)
        led.value(0)