我不明白为什么pygame.transform.rotate函数在我的代码中不起作用

Question

如果我按向右或向左键，图像不会旋转但会变大。我不知道原因。

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class Player(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.Surface((20,40))
        self.image.fill(RED)
        self.rect = self.image.get_rect()
        self.rect.center = (WIDTH/2,HEIGHT/2)
        self.speed = 0
        self.anglesp = 0
        self.angle = 0


    def update(self):
        print(self.angle)
        self.speed = 0
        self.anglesp = 0


        ######  why is this not working?
        self.image = pygame.transform.rotate(self.image, math.radians(self.angle))
        ######

        keystate=pygame.key.get_pressed()
        if keystate[pygame.K_LEFT]:
            self.anglesp = -5

        if keystate[pygame.K_RIGHT]:
            self.anglesp = 5

        self.angle+=self.anglesp

        if self.angle>=360:
            self.angle = 0
        if self.angle<=-360:
            self.angle = 0

all_sprites = pygame.sprite.Group()
fox = Player()
all_sprites.add(fox)

running = True
while running:
    #event
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
    #update

    all_sprites.update()
    #render
    screen.fill(BLACK)
    all_sprites.draw(screen)
    pygame.display.update()
    #clock
    clock.tick(FPS)

pygame.quit()

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