猫史档案馆

# coding:utf-8
import pygame
import time

# pygame初始化
pygame.init()
canvas = pygame.display.set_mode((800, 600))
pygame.display.set_caption("文明")
EarthWorld = []
resources = [0,0,0]#[0]电能 [1]粮食[2]铁
window = ['100','100',EarthWorld,resources]#window[0]和window[1]为部落大小的长和宽
w = str(window)
#定义函数资源
def time():
    for i in EarthWorld:
        if i == 'water':
            return
        elif i == 'sun':
            resources[0] += 1
    time.sleep(1)

# 导入 / 判断存档
with open('存档.txt', 'r', encoding='utf-8') as f:
    content = f.read()

if not content:
    with open('存档.txt', 'w', encoding='utf-8') as f:
        f.write(str(window))  # 需要用 str() 转换为字符串后再写入文件
else:
    window = eval(content)  # 注意使用 eval() 将字符串转换为列表

#加载图片
bg = pygame.image.load('images/bg.png')
bg_x = [0]
bg_y = [0]
# 主循环
while True:
    canvas.blit(bg,(bg_x[0],bg_y[0]))

    #设置背景移动
    if event.type == pygame.KEYDOWN:
        i = 0
        if event.key == pygame.K_w:
            for ba in bg_y:
                if ba >= 600:
                    bg_y[i] = -600
                else:
                    bg_y[i] -= 5
                i += 1
        elif event.key == pygame.K_s:
            for ba in bg_y:
                if ba <= -600:
                    bg_y[i] = 600
                else:
                    bg_y[i] += 5
                i += 1
        elif event.key == pygame.K_a:
            for ba in bg_x:
                if ba >= 600:
                    bg_x[i] = -800
                else:
                    bg_x[i] -= 5
                i += 1
    # 设置窗口关闭
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            exit()
    # 设置窗口主循环
    pygame.display.update()

报错信息：

D:\L1A\venv\Scripts\python.exe C:/Users/Administrator/Desktop/文明/主界面/主界面.py
pygame 2.1.0 (SDL 2.0.16, Python 3.6.5)
Hello from the pygame community. https://www.pygame.org/contribute.html
Traceback (most recent call last):
  File "C:/Users/Administrator/Desktop/文明/主界面/主界面.py", line 41, in <module>
    if event.type == pygame.KEYDOWN:
NameError: name 'event' is not defined

进程已结束,退出代码1

背景