pygame blit函数

import pygame
import random
import itertools
import sys

SCREENWIDE = 822
SCREENHEIGHT = 199
FPS = 30  

class MyMap():

    def __init__(self, x, y):
        # 加载背景图片
        self.bg = pygame.image.load("image/bg.png").convert_alpha()
        self.x = x
        self.y = y

    def map_rolling(self):
        if self.x < -790:  # 小于-790说明地图已经完全移动完毕
            self.x = 800  # 给地图一个新的坐标点
        else:
            self.x -= 5  # 5个像素向左移动

    # 更新地图
    def map_update(self):
        SCREEN.blit(self.bg, (self.x, self.y))

def mainGame():
    score = 0
    over = False
    global SCREEN, FPSCLOCK  
    pygame.init()  # 初始化
    FPSCLOCK = pygame.time.Clock()
    SCREEN = pygame.display.set_mode((SCREENWIDE, SCREENHEIGHT))  # 设置窗体大小
    pygame.display.set_caption('玛丽冒险')  # 窗体标题
    bg1 = MyMap(0, 0)
    bg2 = MyMap(800, 0)
    while True:
        for event in pygame.event.get():  # 循环监听
            if event == pygame.quit():
                pygame.quit()
                sys.exit()
        if over == False:
               bg1.map_update()
               bg1.map_rolling()
               bg2.map_update()
               bg2.map_rolling()
     

if __name__ == '__main__':
    mainGame()

抄了一个pygame的案例，在使用blit函数让地图移动的时候为什么会报错啊

if event == pygame.quit():
这句写错了，quit()是退出pygame，等于你还没运行，就把程序关了
应该写成
if event.type == pygame.QUIT: