“Game Over” 屏幕
主循环顶部 添加 game_over 变量，标记游戏结束状态 
show_go_screen() 函数稍后定义
重置所有内容

# 游戏主循环
game_over = True
running = True
while running:
    if game_over:
        show_go_screen()
        game_over = False
        all_sprites = pygame.sprite.Group()
        mobs = pygame.sprite.Group()
        bullets = pygame.sprite.Group()
        powerups = pygame.sprite.Group()
        player = Player()
        all_sprites.add(player)
        for i in range(8):
            newmob()
        score = 0

当玩家生命值为0，设置 game_over = True

# 如果玩家死亡 并且 爆炸动画播放完毕。
    if player.lives==0 and not death_explosion.alive():
        game_over = True

Game Over 屏幕
添加 show_go_screen() 函数

def show_go_screen():
    screen.blit(background, background_rect)
    draw_text(screen, "太空狙击!", 64, WIDTH / 2, HEIGHT / 4)
    draw_text(screen, "方向键 移动，空格键 开火", 22,
              WIDTH / 2, HEIGHT / 2)
    draw_text(screen, "按任意键开始", 18, WIDTH / 2, HEIGHT * 3 / 4)
    pygame.display.flip()
    waiting = True
    while waiting:
        clock.tick(FPS)
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                pygame.quit()
            if event.type == pygame.KEYUP:
                waiting = False

更多创意：
更多道具，敌人攻击，Boss，关卡