CircuitPython NeoPixel rainbow on a Pico

# CircuitPython on a Raspberry Pi Pico: a NeoPixel rainbow.
# Eight WS2812 LEDs on GP16, driven by Adafruit's neopixel library (which
# the editor puts in lib/ for you) through the Pico's PIO.
import board
import neopixel
import time

pixels = neopixel.NeoPixel(board.GP16, 8, brightness=0.3, auto_write=False)

def wheel(pos):
    # 0 to 255 around the color wheel: red, green, blue and back to red.
    if pos < 85:
        return (255 - pos * 3, pos * 3, 0)
    if pos < 170:
        pos -= 85
        return (0, 255 - pos * 3, pos * 3)
    pos -= 170
    return (pos * 3, 0, 255 - pos * 3)

print("Rainbow on 8 NeoPixels")
step = 0
while True:
    for i in range(8):
        pixels[i] = wheel((i * 32 + step) % 256)
    pixels.show()
    if step % 64 == 0:
        print("step", step, "first pixel", pixels[0])
    step = (step + 4) % 256
    time.sleep(0.02)