A really crap Tamagotchi for micro:bit

crapamagotchi.py

# Make the display sparkle. Click button A to show an image for
# a moment before the sparkles start again. Click button B to
# scroll a friendly message before the sparkles return.
# By Nicholas H.Tollervey and released to the Public Domain.
# How would you improve this code?
from microbit import *
import random

# A full list of images can be found here: http://bit.ly/1WY221q
images = [Image.HAPPY, Image.SAD, Image.GHOST, Image.SKULL,
          Image.DUCK, Image.UMBRELLA, Image.GIRAFFE, Image.RABBIT,
          Image.HEART, Image.ANGRY, Image.STICKFIGURE]

while True:
    sleep(20)
    x = random.randint(0, 4)
    y = random.randint(0, 4)
    brightness = random.randint(0, 9)
    display.set_pixel(x, y, brightness)
    if button_a.was_pressed():
        display.show(random.choice(images))
        sleep(500)
    if button_b.was_pressed():
        display.scroll("Hello, World!", delay=100)