这是我的代码 在 Class Ball 中，我的get_rect（）方法出错了

pygame.init()
pygame.mixer.init()

size = h,w = 500,500

screen = pygame.display.set_mode(size)
black=0,0
gameover=False
image_ball=pygame.image.load('ball.png')
class Ball(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.transform.scale(image_ball,(50,50))

        self.ball_rect = self.image.get_rect()
        self.ball_rect.x = random.randrange(w-self.ball_rect.width)
        self.ball_rect.y = random.randrange(-100,100)
        self.x_speed=5
        self.y_speed=5
    def update(self):
        self.ball_rect.x+=self.x_speed
        if self.ball_rect.right<w:
            self.ball_rect.right=w
        if self.ball_rect.left<0:
            self.ball_rect.left=0
all_sprite=pygame.sprite.Group()
ball_sprite = pygame.sprite.Group()
ball = Ball()
all_sprite.add(ball)
for i in range(10):
    b=Ball()
    ball_sprite.add(b)
    all_sprite.add(b)
while not gameover:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            gameover = True
    all_sprite.update()
    #draw/render
    screen.fill(black)
    ball_sprite.draw(screen)
    pygame.display.flip()
    pygame.time.wait(10)
sys.exit()

我在绘制self.spritedict [spr] = surface_blit（spr.image，spr.rect）时出错

AttributeError：“球”对象没有属性“矩形”