from machine import Pin
from time import sleep

led_pins=[16,17,18,19,21,22,23]

leds = [Pin(pin,Pin.OUT) for pin in led_pins]

while True:
    for i in range(7):
        leds[i].value(1)
        sleep(0.2)
        leds[i].value(0)

    for i in range(6,-1,-1):
        leds[i].value(1)
        sleep(0.2)
        leds[i].value(0)