贪吃蛇是一款经典的小游戏。初始是像素版本，后来又衍生出3D版本、多人对战版本等。玩家使用方向键操控一条长长的蛇不断吞下豆子，同时蛇身随着吞下的豆子不断变长，当蛇头撞到蛇身或障壁时游戏结束。

本文分享在 Python Tkinter 中创建一个流行的可以计分的贪吃蛇游戏代码。

代码中使用了 tkinter、random 、Pillow 三个库，以及一张 PNG 图片作为豆子，图片是名为 game.png，长宽均为 13px 的黑色方块，请自行准备。

from tkinter import *
from random import randint
from PIL import Image, ImageTk

movement = 20
steps_per_sec = 10
speed = 1100 // steps_per_sec

class Snake(Canvas):
    def __init__(self):
        super().__init__(
            width=700, 
            height=400, 
            background='#53ff1a', 
            highlightthickness=0
        )

        self.snake_pos = [(100, 80), (80, 100), (80, 100)]
        self.food_pos = self.set_new_food_pos()
        self.direction = 'Right'
        self.score = 0
        self.load_img()
        self.create_objects()
        self.bind_all('', self.on_key_press)
        self.pack()
        self.after(speed, self.perform_actions)

    def load_img(self):
        try:
            self.snake_body = ImageTk.PhotoImage(Image.open('game.png'))
            self.food = ImageTk.PhotoImage(Image.open('game.png'))
        except IOError as error:
            ws.destroy()
            raise

    def create_objects(self):
        self.create_text(
            35, 
            12, 
            text=f'得分: {self.score}', 
            tag='score', 
            fill='black', 
            font=10
        )

        for x_position, y_position in self.snake_pos:
            self.create_image(
                x_position, 
                y_position, 
                image=self.snake_body, 
                tag='snake'
            )

        self.create_image(
            *self.food_pos, 
            image=self.food, 
            tag='food'
            )
        self.create_rectangle(
            7, 
            27, 
            690, 
            690, 
            outline='#d9d8d7'
            )

    def finish_game(self):
        self.delete(ALL)
        self.create_text(
            self.winfo_width() / 2,
            self.winfo_height() / 2,
            text=f'游戏结束，得分：{self.score}!',
            fill='black',
            font=20
        )

    def consume_food(self):
        if self.snake_pos[0] == self.food_pos:
            self.score += 10
            self.snake_pos.append(self.snake_pos[-1])

            self.create_image(
                *self.snake_pos[-1], 
                image=self.snake_body, 
                tag='snake'
            )
            self.food_pos = self.set_new_food_pos()
            self.coords(
                self.find_withtag('food'), 
                *self.food_pos
                )

            score = self.find_withtag('score')
            self.itemconfigure(
                score, 
                text=f'得分: {self.score}', 
                tag='score'
                )
    
    def boundry(self):
        head_x_position, head_y_position = self.snake_pos[0]

        return (
            head_x_position in (0, 700)
            or head_y_position in (20, 400)
            or (head_x_position, head_y_position) in self.snake_pos[1:]
        )

    def snake_movement(self):
        head_x_position, head_y_position = self.snake_pos[0]

        if self.direction == 'Left':
            new_head_position = (head_x_position - movement, head_y_position)
        elif self.direction == 'Right':
            new_head_position = (head_x_position + movement, head_y_position)
        elif self.direction == 'Down':
            new_head_position = (head_x_position, head_y_position + movement)
        elif self.direction == 'Up':
            new_head_position = (head_x_position, head_y_position - movement)

        self.snake_pos = [new_head_position] + self.snake_pos[:-1]

        for segment, position in zip(self.find_withtag('snake'), self.snake_pos):
            self.coords(segment, position)

    def on_key_press(self, e):
        new_direction = e.keysym

        all_directions = (
            'Up', 
            'Down', 
            'Left', 
            'Right'
            )
        opposites = (
            {'Up', 'Down'}, 
            {'Left', 'Right'}
            )

        if (
            new_direction in all_directions
            and {new_direction, self.direction} not in opposites
        ):
            self.direction = new_direction

    def perform_actions(self):
        if self.boundry():
            self.finish_game()

        self.consume_food()
        self.snake_movement()

        self.after(speed, self.perform_actions)

    def set_new_food_pos(self):
        while True:
            x_position = randint(1, 29) * movement
            y_position = randint(3, 30) * movement
            food_pos = (x_position, y_position)

            if food_pos not in self.snake_pos:
                return food_pos

ws = Tk()
ws.title('贪吃蛇')
ws.resizable(False, False)
board = Snake()
ws.mainloop()