Мини-проект: прыгающий мяч

import pygame

SHIRINA, VYSOTA = 600, 400
RADIUS = 20

pygame.init()
screen = pygame.display.set_mode((SHIRINA, VYSOTA))
clock = pygame.time.Clock()

x, y = SHIRINA // 2, VYSOTA // 2
dx, dy = 4, 3

rabotaet = True
while rabotaet:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            rabotaet = False

    x += dx
    y += dy

    if x - RADIUS < 0 or x + RADIUS > SHIRINA:
        dx = -dx
    if y - RADIUS < 0 or y + RADIUS > VYSOTA:
        dy = -dy

    screen.fill((20, 20, 40))
    pygame.draw.circle(screen, (255, 100, 100), (int(x), int(y)), RADIUS)
    pygame.display.flip()
    clock.tick(60)

pygame.quit()