def item_effect(event,ai_settings,screen,stats,aliens,ship_bullets,items):
    if event.key == pygame.K_1 and stats.item_1 - len(ai_settings.timekeep[1]) > 0:
        ai_settings.ship_bullet_width *= 8 # 飞船子弹宽度乘以 8
        ai_settings.timekeep[1].append((time()))
    elif event.key == pygame.K_2 and stats.item_2 - len(ai_settings.timekeep[2]) > 0:
        ai_settings.floating_drop_speed /= 2 # 外星人下降速度除以 2
        ai_settings.timekeep[2].append((time()))
    elif event.key == pygame.K_3 and stats.item_3 - len(ai_settings.timekeep[3]) > 0:
        ai_settings.energy_bullet = False # 普通子弹升级为高能子弹
        ai_settings.timekeep[3].append((time()))
    elif event.key == pygame.K_4 and stats.item_4 - len(ai_settings.timekeep[4]) > 0:
        stats.killed_number += len(aliens.sprites())
        stats.score += len(aliens.sprites()) * ai_settings.alien_points
        stats.item_4 -= 1
        aliens.empty()
        ship_bullets.empty() # 清除屏幕上所有外星人
        #refactor  两个if单独定义函数
        if stats.killed_number // ai_settings.award_base > Item.count:
            item = Item(ai_settings,screen)
            item.caculate_number()
            items.add(item)
        if stats.killed_number // ai_settings.level_base > stats.level:
            if stats.level < 20:
                ai_settings.increase_speed()
                stats.level += 1
    elif event.key == pygame.K_5 and stats.item_5 - len(ai_settings.timekeep[5]) > 0:
        ai_settings.effect_time *= 2
        ai_settings.timekeep[5].append((time()))
    elif event.key == pygame.K_6 and stats.item_6 - len(ai_settings.timekeep[6]) > 0:
        ai_settings.timekeep[6].append(time())
def check_bullet_alien_collisions(ai_settings,screen,stats,ship,aliens,ship_bullets,items):
    '''响应子弹与外星人的碰撞'''
    # 检查是否有子弹击中了外星人,如果是,就删除相应的子弹和外星人
    collisions = pygame.sprite.groupcollide(ship_bullets,aliens,ai_settings.energy_bullet,True)

    # 计分
    if collisions:
        for aliens_hit in collisions.values():
            stats.killed_number += len(aliens_hit)
            stats.bullet_killed_number += len(aliens_hit)
            stats.score += ai_settings.alien_points * len(aliens_hit)
            #refactor  两个if单独定义函数
            if stats.killed_number // ai_settings.award_base > Item.count:
                item = Item(ai_settings,screen)
                item.caculate_number()
                items.add(item)
            if stats.killed_number // ai_settings.level_base > stats.level:
                if stats.level < 20:
                    ai_settings.increase_speed()
                    stats.level += 1