我试着把我学到的东西用来构建蛇游戏python，但它不起作用

import pygame
import random

# 初始化游戏
pygame.init()

# 定义游戏窗口的大小
window_width = 800
window_height = 600

# 创建游戏窗口
window = pygame.display.set_mode((window_width, window_height))
pygame.display.set_caption("Snake Game")

# 定义蛇的初始位置和大小
snake_size = 20
snake_x = window_width / 2
snake_y = window_height / 2

# 定义蛇的移动速度
snake_speed = 10

# 定义蛇的移动方向
snake_direction = "RIGHT"

# 定义食物的初始位置
food_x = round(random.randrange(0, window_width - snake_size) / 20.0) * 20.0
food_y = round(random.randrange(0, window_height - snake_size) / 20.0) * 20.0

# 游戏主循环
running = True
while running:
    # 处理游戏事件
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False

    # 获取键盘输入，控制蛇的移动方向
    keys = pygame.key.get_pressed()
    if keys[pygame.K_LEFT]:
        snake_direction = "LEFT"
    elif keys[pygame.K_RIGHT]:
        snake_direction = "RIGHT"
    elif keys[pygame.K_UP]:
        snake_direction = "UP"
    elif keys[pygame.K_DOWN]:
        snake_direction = "DOWN"

    # 根据蛇的移动方向更新蛇的位置
    if snake_direction == "LEFT":
        snake_x -= snake_speed
    elif snake_direction == "RIGHT":
        snake_x += snake_speed
    elif snake_direction == "UP":
        snake_y -= snake_speed
    elif snake_direction == "DOWN":
        snake_y += snake_speed

    # 绘制游戏窗口和蛇
    window.fill((0, 0, 0))
    pygame.draw.rect(window, (255, 0, 0), (food_x, food_y, snake_size, snake_size))
    pygame.draw.rect(window, (0, 255, 0), (snake_x, snake_y, snake_size, snake_size))
    pygame.display.update()

# 退出游戏
pygame.quit()