各位大佬，帮我看下move（）错在哪里，pygame运行报错

import  pygame,sys
pygame.init()
screen = pygame.display.set_mode([640,640])
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)
        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-free-png-210x210.png",[10,0],[20,20])
running = True
while running:
    for event in  pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
    clock.tick(30)
    screen.blit(background,(0,0))
    my_ball.move()
    screen.blit(my_ball.image,my_ball.rect)
    pygame.display.flip()
pygame.quit()