from machine import Pin
from utime import sleep, sleep_ms

b1 = Pin(15, Pin.OUT)
b2 = Pin(2, Pin.OUT)
b3 = Pin(4, Pin.OUT)
b4 = Pin(16, Pin.OUT)
b5 = Pin(17, Pin.OUT)
b6 = Pin(5, Pin.OUT)
b7 = Pin(18, Pin.OUT)
b8 = Pin(19, Pin.OUT)

leds = [b1, b2, b3, b4, b5, b6, b7, b8]

while True:
    for i in leds[::1]:
        i.on()
        sleep_ms(50)
        i.off()
        sleep_ms(50)
    for i in leds[::-1]:
        i.on()
        sleep_ms(50)
        i.off()
        sleep_ms(50)