点击按钮改变标签的内容

from Tkinter import*def click_up():    counter.set(counter.get()+1)def click_down():    counter.set(counter.get()-1)#if __name__= "__main__":window=Tk()counter=IntVar()counter.set(0)frame=Frame(window)frame.pack()button1=Button(frame,text='UP',command=click_up)button1.pack()button2=Button(frame,text='DOWN',command=click_down)button2.pack()label=Label(frame,textvariable=counter)label.pack()window.mainloop()