Anthony - Multi-Coloured Bouncing Balls

import random
import pygame

class ball:
    def __init__(s):
        s.x = random.randint(0, ds[0])
        s.y = random.randint(0, ds[1])

        s.dx = random.uniform(0.01, 2) * [-1, 1][random.randint(0, 1)]
        s.dy = random.uniform(0.01, 2) * [-1, 1][random.randint(0, 1)]

        s.color = (random.randint(0, 255), random.randint(0, 255), random.randint(0, 255))

    def update(s):
        pygame.draw.circle(display, s.color, (s.x, s.y), 25)

        s.x += s.dx
        s.y += s.dy

        if s.x + 25 > ds[0]:
            s.x = ds[0] - 25
            s.dx = -s.dx
        if s.x < 25:
            s.x = 25
            s.dx = -s.dx

        if s.y + 25 > ds[1]:
            s.y = ds[1] - 25
            s.dy = -s.dy
        if s.y < 25:
            s.y = 25
            s.dy = -s.dy

pygame.init()
display = pygame.display.set_mode((800, 600))
ds = display.get_rect().size
# ds = width and height

BLACK = (0, 0, 0)
WHITE = (255, 255, 255)


balls = list([ball() for _ in range(50)])

exit_demo = False
while not exit_demo:
    events = pygame.event.get()
    for event in events:
        if event.type == pygame.KEYUP and event.key == pygame.K_ESCAPE:
            exit_demo = True

    display.fill(BLACK)

    for b in balls:
        b.update()

    pygame.display.update()
    pygame.time.Clock().tick(120)

# this is outside of the main game loop. So after ESCAPE is pressed!
if 1 == 0:
    print("true")