帮我用python写一个贪吃蛇

好的，以下是一个简单的贪吃蛇游戏代码示例：

import pygame
import random

# 全局变量
SCREEN_WIDTH = 600
SCREEN_HEIGHT = 600
BLOCK_SIZE = 20

# 蛇类
class Snake:
    def __init__(self):
        self.body = [(SCREEN_WIDTH/2, SCREEN_HEIGHT/2)]
        self.direction = 'right'
        self.score = 0
        self.is_dead = False
    
    # 移动蛇
    def move(self):
        head = self.body[0]
        if self.direction == 'right':
            new_head = (head[0] + BLOCK_SIZE, head[1])
        elif self.direction == 'left':
            new_head = (head[0] - BLOCK_SIZE, head[1])
        elif self.direction == 'up':
            new_head = (head[0], head[1] - BLOCK_SIZE)
        elif self.direction == 'down':
            new_head = (head[0], head[1] + BLOCK_SIZE)
        self.body.insert(0, new_head)
        self.body.pop()
    
    # 改变方向
    def change_direction(self, direction):
        if direction == 'right' and self.direction != 'left':
            self.direction = 'right'
        elif direction == 'left' and self.direction != 'right':
            self.direction = 'left'
        elif direction == 'up' and self.direction != 'down':
            self.direction = 'up'
        elif direction == 'down' and self.direction != 'up':
            self.direction = 'down'
    
    # 吃食物
    def eat_food(self, food):
        if self.body[0] == food.position:
            self.body.insert(0, food.position)
            self.score += 1
            return True
        return False
    
    # 检测是否撞墙或自身
    def check_collision(self):
        head = self.body[0]
        if head[0] < 0 or head[0] >= SCREEN_WIDTH or head[1] < 0 or head[1] >= SCREEN_HEIGHT:
            self.is_dead = True
        for block in self.body[1:]:
            if head == block:
                self.is_dead = True

# 食物类
class Food:
    def __init__(self):
        self.position = self.generate_position()
    
    # 生成随机位置
    def generate_position(self):
        x = random.randint(0, SCREEN_WIDTH/BLOCK_SIZE - 1) * BLOCK_SIZE
        y = random.randint(0, SCREEN_HEIGHT/BLOCK_SIZE - 1) * BLOCK_SIZE
        return (x, y)
    
    # 重新生成位置
    def regenerate(self):
        self.position = self.generate_position()

# 主函数
def main():
    # 初始化
    pygame.init()
    pygame.display.set_caption('贪吃蛇')
    screen = pygame.display.set_mode((SCREEN_WIDTH, SCREEN_HEIGHT))
    clock = pygame.time.Clock()
    font = pygame.font.SysFont('Arial', 30)
    snake = Snake()
    food = Food()
    
    # 游戏循环
    while True:
        # 处理事件
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                pygame.quit()
                return
            elif event.type == pygame.KEYDOWN:
                if event.key == pygame.K_RIGHT:
                    snake.change_direction('right')
                elif event.key == pygame.K_LEFT:
                    snake.change_direction('left')
                elif event.key == pygame.K_UP:
                    snake.change_direction('up')
                elif event.key == pygame.K_DOWN:
                    snake.change_direction('down')
        
        # 移动蛇
        snake.move()
        
        # 检测是否吃到食物
        if snake.eat_food(food):
            food.regenerate()
        
        # 检测是否撞墙或自身
        snake.check_collision()
        
        # 绘制画面
        screen.fill((255, 255, 255))
        for block in snake.body:
            pygame.draw.rect(screen, (0, 255, 0), (block[0], block[1], BLOCK_SIZE, BLOCK_SIZE))
        pygame.draw.rect(screen, (255, 0, 0), (food.position[0], food.position[1], BLOCK_SIZE, BLOCK_SIZE))
        score_text = font.render('Score: ' + str(snake.score), True, (0, 0, 0))
        screen.blit(score_text, (10, 10))
        if snake.is_dead:
            game_over_text = font.render('Game Over', True, (255, 0, 0))
            screen.blit(game_over_text, (SCREEN_WIDTH/2 - 80, SCREEN_HEIGHT/2))
        
        pygame.display.update()
        clock.tick(10)

if __name__ == '__main__':
    main()

你可以将代码保存为一个名为 `snake.py` 的文件，然后在命令行中运行 `python snake.py` 来启动游戏。