Python tkinter 用键盘移动没反映修改代码

from tkinter import *

 

def movetriangle(event):

    if event.keysym == 'Up':

        canvas.move(a1,0,-3)

    elif event.keysym == 'Down':

        canvas.move(a1,0,3)

    elif event.keysym == 'Left':

        canvas.move(a1,-3,0)

    elif event.keysym == 'Right':

        canvas.move(a1,3,0)

 

tk=Tk()

canvas=Canvas(tk,width=400,height=400)

a1=canvas.create_polygon(10,10,10,60,50,35)

canvas.bind_all('<KeyPress-Up>',movetriangle)

canvas.bind_all('<KeyPress-Down>',movetriangle)

canvas.bind_all('<KeyPress-Left>',movetriangle)

canvas.bind_all('<KeyPress-Right>',movetriangle)

canvas.pack()