用python中的pygame库写一个贪吃蛇游戏，游戏规则如下：

好的，以下是一个简单的贪吃蛇游戏代码：

import pygame
import random

# 初始化pygame
pygame.init()

# 定义一些常量
WIDTH = 600
HEIGHT = 480
GRID_SIZE = 20
SPEED = 10

# 创建游戏窗口
screen = pygame.display.set_mode((WIDTH, HEIGHT))
pygame.display.set_caption("贪吃蛇")

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

# 定义贪吃蛇类
class Snake:
    def __init__(self):
        self.body = [(WIDTH / 2, HEIGHT / 2)]
        self.direction = random.choice(["up", "down", "left", "right"])

    def move(self):
        if self.direction == "up":
            self.body.insert(0, (self.body[0][0], self.body[0][1] - GRID_SIZE))
        elif self.direction == "down":
            self.body.insert(0, (self.body[0][0], self.body[0][1] + GRID_SIZE))
        elif self.direction == "left":
            self.body.insert(0, (self.body[0][0] - GRID_SIZE, self.body[0][1]))
        elif self.direction == "right":
            self.body.insert(0, (self.body[0][0] + GRID_SIZE, self.body[0][1]))

        # 删除尾部
        self.body.pop()

    def draw(self):
        for pos in self.body:
            pygame.draw.rect(screen, GREEN, (pos[0], pos[1], GRID_SIZE, GRID_SIZE))

    def check_collision(self):
        # 检查是否碰到边界
        if self.body[0][0] < 0 or self.body[0][0] >= WIDTH or self.body[0][1] < 0 or self.body[0][1] >= HEIGHT:
            return True

        # 检查是否碰到自己
        for pos in self.body[1:]:
            if pos == self.body[0]:
                return True

        return False

    def change_direction(self, direction):
        if direction == "up" and self.direction != "down":
            self.direction = "up"
        elif direction == "down" and self.direction != "up":
            self.direction = "down"
        elif direction == "left" and self.direction != "right":
            self.direction = "left"
        elif direction == "right" and self.direction != "left":
            self.direction = "right"

# 定义食物类
class Food:
    def __init__(self):
        self.pos = (random.randint(0, WIDTH // GRID_SIZE - 1) * GRID_SIZE,
                    random.randint(0, HEIGHT // GRID_SIZE - 1) * GRID_SIZE)

    def draw(self):
        pygame.draw.rect(screen, RED, (self.pos[0], self.pos[1], GRID_SIZE, GRID_SIZE))

# 创建贪吃蛇和食物对象
snake = Snake()
food = Food()

# 游戏循环
clock = pygame.time.Clock()
running = True
while running:
    # 设置帧率
    clock.tick(SPEED)

    # 处理事件
    for event in pygame.event.get():
        if event.type == pygame.QUIT:
            running = False
        elif event.type == pygame.KEYDOWN:
            if event.key == pygame.K_UP:
                snake.change_direction("up")
            elif event.key == pygame.K_DOWN:
                snake.change_direction("down")
            elif event.key == pygame.K_LEFT:
                snake.change_direction("left")
            elif event.key == pygame.K_RIGHT:
                snake.change_direction("right")

    # 移动贪吃蛇
    snake.move()

    # 检查是否碰撞
    if snake.check_collision():
        running = False

    # 检查是否吃到食物
    if snake.body[0] == food.pos:
        snake.body.append(snake.body[-1])
        food = Food()

    # 绘制游戏界面
    screen.fill(BLACK)
    snake.draw()
    food.draw()
    pygame.display.update()

# 退出游戏
pygame.quit()

这个代码实现了一个基本的贪吃蛇游戏，可以通过上下左右键来控制贪吃蛇的移动方向，当贪吃蛇碰到边界或者自己时游戏结束。