Chapter 13 Pygame ball

import sys
import pygame 
pygame.init()
size = width, height = 640,480
screen = pygame.display.set_mode(size) 
color = (0,0,0)
ball = pygame.image.load("th.jpg") 
ballrect = ball.get_rect() 
speed = [5,5]
clock = pygame.time.Clock() 
while True:
    clock.tick(60)
    for event in pygame.event.get():
        if event.type == pygame.QUIT: 
            sys.exit()
    ballrect = ballrect.move(speed)
    if ballrect.left <0 or ballrect.right > width:
        speed[0] = -speed[1]
    if ballrect.top <0 or ballrect.bottom > height:
        speed[1] = -speed[1] 
    screen.fill(color)
    screen.blit(ball, ballrect) 
    pygame.display.flip() 
pygame.quit()