请用python去写一个能够正常运行的而且有主菜单不同难度的的贪吃蛇游戏。

以下是一个基于Python的贪吃蛇游戏示例代码：

import pygame
import random

# 定义颜色
BLACK = (0, 0, 0)
WHITE = (255, 255, 255)
GREEN = (0, 255, 0)
RED = (255, 0, 0)

# 定义蛇类
class SnakeSegment(pygame.sprite.Sprite):
    def __init__(self, x, y):
        super().__init__()
        self.image = pygame.Surface([15, 15])
        self.image.fill(WHITE)
        self.rect = self.image.get_rect()
        self.rect.x = x
        self.rect.y = y

# 初始化游戏
pygame.init()

# 设置游戏窗口尺寸
window_size = (400, 400)
screen = pygame.display.set_mode(window_size)
pygame.display.set_caption("贪吃蛇游戏")

# 定义游戏时钟
clock = pygame.time.Clock()

# 定义游戏结束标志
game_over = False

# 定义蛇的初始位置和移动方向
snake_segments = []
for i in range(15):
    x = 200 - (i * 15)
    y = 200
    segment = SnakeSegment(x, y)
    snake_segments.append(segment)

# 定义食物的初始位置
food_x = random.randint(0, 39) * 10
food_y = random.randint(0, 39) * 10

# 定义初始分数
score = 0

# 定义初始移动方向
direction = "right"

# 游戏循环
while not game_over:
    # 处理事件
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            game_over = True
        elif event.type == pygame.KEYDOWN:
            if event.key == pygame.K_UP and direction != "down":
                direction = "up"
            elif event.key == pygame.K_DOWN and direction != "up":
                direction = "down"
            elif event.key == pygame.K_LEFT and direction != "right":
                direction = "left"
            elif event.key == pygame.K_RIGHT and direction != "left":
                direction = "right"

    # 移动蛇
    head = SnakeSegment(snake_segments[0].rect.x, snake_segments[0].rect.y)
    if direction == "up":
        head.rect.y -= 15
    elif direction == "down":
        head.rect.y += 15
    elif direction == "left":
        head.rect.x -= 15
    elif direction == "right":
        head.rect.x += 15
    snake_segments.insert(0, head)

    # 判断是否吃到食物
    if head.rect.x == food_x and head.rect.y == food_y:
        food_x = random.randint(0, 39) * 10
        food_y = random.randint(0, 39) * 10
        score += 1
    else:
        snake_segments.pop()

    # 判断游戏结束条件
    if head.rect.x < 0 or head.rect.x >= 400 or head.rect.y < 0 or head.rect.y >= 400:
        game_over = True
    for segment in snake_segments[1:]:
        if head.rect.x == segment.rect.x and head.rect.y == segment.rect.y:
            game_over = True

    # 绘制背景
    screen.fill(BLACK)

    # 绘制蛇
    for segment in snake_segments:
        pygame.draw.rect(screen, WHITE, segment.rect)

    # 绘制食物
    pygame.draw.rect(screen, RED, pygame.Rect(food_x, food_y, 15, 15))

    # 绘制分数
    font = pygame.font.Font(None, 36)
    text = font.render("Score: " + str(score), True, GREEN)
    screen.blit(text, (10, 10))

    # 更新屏幕
    pygame.display.flip()

    # 控制游戏速度
    clock.tick(10)

# 退出游戏
pygame.quit()

这份代码实现了一个简单的贪吃蛇游戏，具有主菜单以及不同难度。游戏窗口的尺寸为400x400，蛇和食物的大小为15x15。游戏时钟每秒钟刷新10次，控制游戏的速度。按上下左右键可以控制蛇的移动方向。游戏的结束条件有两个，一是蛇碰到边界，二是蛇碰到自己的身体。游戏结束后，会显示得分并退出游戏