写一个贪吃蛇小游戏代码

以下是Python语言的贪吃蛇小游戏代码：

import pygame
import random

# 初始化pygame
pygame.init()

# 设置窗口大小和标题
screen_width = 640
screen_height = 480
screen = pygame.display.set_mode((screen_width, screen_height))
pygame.display.set_caption("贪吃蛇小游戏")

# 定义颜色
white = (255, 255, 255)
black = (0, 0, 0)
red = (255, 0, 0)
green = (0, 255, 0)

# 定义方向
UP = 1
DOWN = 2
LEFT = 3
RIGHT = 4

# 定义蛇类
class Snake():
    def __init__(self):
        self.length = 1
        self.positions = [(screen_width / 2, screen_height / 2)]
        self.direction = random.choice([UP, DOWN, LEFT, RIGHT])
        self.color = green
        
    def get_head_position(self):
        return self.positions[0]
    
    def turn(self, point):
        if self.length > 1 and (point[0]*-1, point[1]*-1) == self.direction:
            return
        else:
            self.direction = point
    
    def move(self):
        cur = self.get_head_position()
        x, y = self.direction
        new = ((cur[0] + (x*10)), (cur[1] + (y*10)))
        if new in self.positions[2:]:
            self.reset()
        else:
            self.positions.insert(0, new)
            if len(self.positions) > self.length:
                self.positions.pop()
                
    def reset(self):
        self.length = 1
        self.positions = [(screen_width / 2, screen_height / 2)]
        self.direction = random.choice([UP, DOWN, LEFT, RIGHT])
        
    def draw(self, surface):
        for p in self.positions:
            r = pygame.Rect((p[0], p[1]), (10, 10))
            pygame.draw.rect(surface, self.color, r)
            pygame.draw.rect(surface, black, r, 1)
            
    def handle_keys(self):
        for event in pygame.event.get():
            if event.type == pygame.QUIT:
                pygame.quit()
                quit()
            elif event.type == pygame.KEYDOWN:
                if event.key == pygame.K_UP:
                    self.turn((0, -1))
                elif event.key == pygame.K_DOWN:
                    self.turn((0, 1))
                elif event.key == pygame.K_LEFT:
                    self.turn((-1, 0))
                elif event.key == pygame.K_RIGHT:
                    self.turn((1, 0))
                
# 定义食物类
class Food():
    def __init__(self):
        self.position = (0, 0)
        self.color = red
        self.randomize_position()
        
    def randomize_position(self):
        self.position = (random.randint(0, screen_width - 10), random.randint(0, screen_height - 10))
        
    def draw(self, surface):
        r = pygame.Rect((self.position[0], self.position[1]), (10, 10))
        pygame.draw.rect(surface, self.color, r)
        pygame.draw.rect(surface, black, r, 1)
        
# 创建蛇和食物对象
snake = Snake()
food = Food()

# 设置游戏时钟
clock = pygame.time.Clock()

# 游戏循环
while True:
    # 处理键盘事件
    snake.handle_keys()
    
    # 移动蛇和检测碰撞
    snake.move()
    if snake.get_head_position() == food.position:
        snake.length += 1
        food.randomize_position()
    snake.draw(screen)
    food.draw(screen)
    
    # 刷新屏幕
    pygame.display.update()
    
    # 设置帧率
    clock.tick(15)
    
# 退出pygame
pygame.quit()

这是一个基本的贪吃蛇游戏，包括蛇类、食物类、处理键盘事件、移动蛇、检测碰撞等各种功能。你可以根据自己的需要添加更多的特性，比如：增加游戏难度、计分、排行榜等等。