这个图片加载不出来

import sys

import pygame

def main():
    #初始化
    pygame.init()

    width,height=480,852

    #屏幕对象
    screen=pygame.display.set_mode((width,height))
    #设置窗口的标题
    pygame.display.set_caption('飞机大战_帅逼余金灿编写')

    #加载背景图片
    bg=pygame.image.load('./assets/images/background.png')

    while True:
        #1.监听事件
        for event in pygame.event.get():
                #退出游戏
                if event.type == pygame.QUIT:
                    pygame.quit()
                    sys.exit()
        #更新游戏的状态
        #回执
        screen.blit(bg,bg.get_rect())
        pygame.display
main()

报错提示：

Traceback (most recent call last):

  File "C:/Users/Think/PycharmProjects/feijidazhan/store/main.py", line 30, in <module>

    main()

  File "C:/Users/Think/PycharmProjects/feijidazhan/store/main.py", line 17, in main

    bg=pygame.image.load('assets/images/background.png')

pygame.error: Couldn't open assets/images/background.png

还有有一个很奇怪的，我一打__双下划线就会变成_ _这样子，不知道咋回事