使用python3 编写一个贪吃蛇游戏，给我完整的代码

好的，以下是使用Python3编写的贪吃蛇游戏的完整代码。代码注释中有详细的说明。

import pygame
import random

# 游戏界面大小和每个方块的大小
WIDTH, HEIGHT = 640, 480
GRID_SIZE = 20

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

class Snake:
    def __init__(self):
        # 初始化蛇的位置
        self.body = [(WIDTH/2, HEIGHT/2), (WIDTH/2-GRID_SIZE, HEIGHT/2), (WIDTH/2-2*GRID_SIZE, HEIGHT/2)]
        # 初始化蛇的移动方向
        self.direction = "right"
        # 初始化蛇是否死亡
        self.is_dead = False

    def move(self):
        # 蛇移动
        head = self.body[0]
        if self.direction == "right":
            new_head = (head[0]+GRID_SIZE, head[1])
        elif self.direction == "left":
            new_head = (head[0]-GRID_SIZE, head[1])
        elif self.direction == "up":
            new_head = (head[0], head[1]-GRID_SIZE)
        elif self.direction == "down":
            new_head = (head[0], head[1]+GRID_SIZE)
        # 判断蛇移动后是否死亡
        if new_head[0] < 0 or new_head[0] >= WIDTH or new_head[1] < 0 or new_head[1] >= HEIGHT:
            self.is_dead = True
        elif new_head in self.body:
            self.is_dead = True
        # 移动蛇
        if not self.is_dead:
            self.body.insert(0, new_head)
            if new_head != self.food:
                self.body.pop()
            else:
                self.add_food()

    def add_food(self):
        # 随机生成食物的位置
        while True:
            x = random.randint(0, WIDTH/GRID_SIZE-1) * GRID_SIZE
            y = random.randint(0, HEIGHT/GRID_SIZE-1) * GRID_SIZE
            if (x, y) not in self.body:
                break
        self.food = (x, y)

    def draw(self, surface):
        # 画出蛇和食物
        for block in self.body:
            pygame.draw.rect(surface, GREEN, (block[0], block[1], GRID_SIZE, GRID_SIZE))
        pygame.draw.rect(surface, RED, (self.food[0], self.food[1], GRID_SIZE, GRID_SIZE))

class Game:
    def __init__(self):
        # 初始化游戏界面
        self.screen = pygame.display.set_mode((WIDTH, HEIGHT))
        pygame.display.set_caption("Snake Game")
        # 初始化蛇和食物
        self.snake = Snake()
        self.snake.add_food()
        # 初始化计时器
        self.clock = pygame.time.Clock()

    def run(self):
        # 游戏循环
        while True:
            # 处理事件
            for event in pygame.event.get():
                if event.type == pygame.QUIT:
                    pygame.quit()
                    quit()
                elif event.type == pygame.KEYDOWN:
                    if event.key == pygame.K_RIGHT and self.snake.direction != "left":
                        self.snake.direction = "right"
                    elif event.key == pygame.K_LEFT and self.snake.direction != "right":
                        self.snake.direction = "left"
                    elif event.key == pygame.K_UP and self.snake.direction != "down":
                        self.snake.direction = "up"
                    elif event.key == pygame.K_DOWN and self.snake.direction != "up":
                        self.snake.direction = "down"
            # 移动蛇
            self.snake.move()
            # 画出蛇和食物
            self.screen.fill(BLACK)
            self.snake.draw(self.screen)
            # 判断游戏是否结束
            if self.snake.is_dead:
                font = pygame.font.Font(None, 36)
                text = font.render("Game Over", True, WHITE)
                self.screen.blit(text, (WIDTH/2-70, HEIGHT/2-18))
                pygame.display.update()
                pygame.time.wait(2000)
                pygame.quit()
                quit()
            # 刷新屏幕
            pygame.display.update()
            # 控制游戏帧率
            self.clock.tick(10)

if __name__ == "__main__":
    pygame.init()
    game = Game()
    game.run()