Python Tkinter -蛇身跟随蛇头的问题

import tkinter as tk

window = tk.Tk()
window.title("贪吃蛇游戏")
window.geometry("400x400")

canvas = tk.Canvas(window, bg="white")
canvas.pack()

snake_head = (100, 100)  # 蛇头初始位置
snake_direction = "right"  # 蛇初始移动方向

snake_body = [(100, 100), (90, 100), (80, 100)]  # 蛇身初始位置

def move_snake():
    global snake_head, snake_body, snake_direction
    
    if snake_direction == "up":
        snake_head = (snake_head[0], snake_head[1] - 10)
    elif snake_direction == "down":
        snake_head = (snake_head[0], snake_head[1] + 10)
    elif snake_direction == "left":
        snake_head = (snake_head[0] - 10, snake_head[1])
    elif snake_direction == "right":
        snake_head = (snake_head[0] + 10, snake_head[1])
    
    snake_body.insert(0, snake_head)
    snake_body.pop()

def on_key_press(event):
    global snake_direction
    
    if event.keysym == "Up" and snake_direction != "down":
        snake_direction = "up"
    elif event.keysym == "Down" and snake_direction != "up":
        snake_direction = "down"
    elif event.keysym == "Left" and snake_direction != "right":
        snake_direction = "left"
    elif event.keysym == "Right" and snake_direction != "left":
        snake_direction = "right"
    
window.bind("<KeyPress>", on_key_press)

def draw():
    canvas.delete("all")
    
    # 绘制蛇的身体
    for body_part in snake_body:
        canvas.create_rectangle(body_part[0], body_part[1], body_part[0] + 10, body_part[1] + 10, fill="green")
    
    # 绘制食物
    canvas.create_oval(food_position[0], food_position[1], food_position[0] + 10, food_position[1] + 10, fill="red")
    
    window.after(100, draw)

def game_loop():
    move_snake()
    draw()
    window.after(100, game_loop)
    
game_loop()