MicroPython meteor light on eight PWM bar segments, on an ESP32-DevKitC V4

# Meteor light: eight bar segments on PWM, a bright head and a tail that
# fades behind it, moving up the bar and back.
from machine import Pin, PWM
import time

pins = [15, 2, 0, 4, 5, 18, 19, 21]
leds = [PWM(Pin(n), freq=10000, duty=0) for n in pins]
tail = [1023, 512, 256, 128, 64, 32, 16, 8]

def show(head, step):
    # step is +1 going up and -1 coming back: the tail trails behind
    for i, led in enumerate(leds):
        behind = (head - i) * step
        led.duty(tail[behind] if 0 <= behind < len(tail) else 0)

while True:
    for head in range(8):
        show(head, 1)
        time.sleep_ms(60)
    for head in range(7, -1, -1):
        show(head, -1)
        time.sleep_ms(60)
    print("meteor")