import pygame, sys                                                    
pygame.init()                                                         
screen = pygame.display.set_mode([640,480])                           
background = pygame.Surface(screen.get_size())                        
background.fill([255, 255, 255])                                      
clock = pygame.time.Clock()                                           
 
class Ball(pygame.sprite.Sprite):                                     
   def __init__(self, image_file, speed, location):                   
        pygame.sprite.Sprite.__init__(self) #call Sprite initializer  
        self.image = pygame.image.load(image_file)                    
        self.rect = self.image.get_rect()                             
        self.rect.left, self.rect.top = location                      
        self.speed = speed                                            
  
   def move(self):                                                    
        if self.rect.left <= screen.get_rect().left or \
                 self.rect.right >= screen.get_rect().right:          
            self.speed[0] = - self.speed[0]                           
        newpos = self.rect.move(self.speed)                           
        self.rect = newpos                                            

my_ball = Ball('beach_ball.png', [10,0], [20, 20])                    
screen.blit(my_ball.image, my_ball.rect)                              

delay = 100
interval = 50
pygame.key.set_repeat(delay, interval)

while True:                                                           
    for event in pygame.event.get():                                  
        if event.type == pygame.QUIT:                                 
            sys.exit()                                                
        elif event.type == pygame.KEYDOWN:                            
            if event.key == pygame.K_UP:                              
                my_ball.rect.top = my_ball.rect.top - 10              
            elif event.key == pygame.K_DOWN:                          
                my_ball.rect.top = my_ball.rect.top + 10              

    clock.tick(30)                                                   
    screen.blit(background, (0, 0))                                   
    my_ball.move()                                                    
    screen.blit(my_ball.image, my_ball.rect)