pygame 程序未报错却黑屏无法显示 请问有大佬知道解决方法吗

以下是从一本书上抄下来稍加改动的源代码，在 Python Idle 里运行没有报错，然而弹出的 pygame 窗口却除了显示窗口标题外一片漆黑

import pygame
import sys

# set everything to where started
pygame.init()

size = width, height = 650, 650
speed = [-2,1]
bg = (255, 255, 255)

# create a window with a determined size
screen = pygame.display.set_mode(size)

# create window title
pygame.display.set_caption("Hello!")

ball = pygame.image.load("D://Python//soccer.jpg")
# position of the image
position = ball.get_rect()

while True:
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            sys.exit()

# move the image
position = position.move(speed)

if position.left < 0 or position.right > height:
    # flip image
    turtle = pygame.transform.flip(ball, True, False)
    # move to the other side
    speed[1] = -speed[1]

if position.top < 0 or position.bottom > height:
    speed[1] = -speed[1]

# fill the background
screen.fill()
# refresh image
screen.blit(ball, position)
# refresh screen
pygame.display.flip()
pygame.display.update()

# 10ms delay
pygame.time.delay(10)