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("ball.png")
ballrect=ball.get_rect()
speed=[5,5]
clock=pygame.time.Clock()
clock=pygame.time.Clock()
while True:
clock.tick(60)
for event in pygame.event.get():
if event.type==pygame.QUIT:
pygame.quit()
sys.exit()

ballrect=ballrect.move(speed)
if ballrect.left<0 or ballrect.right>width:
speed[0]=-speed[0]
if ballrect.top<0 or ballrect.bottom>height:
speed[1]=-speed[1]
screen.fill(color)
screen.blit(ball,ballrect)
pygame.display.flip()