一个关于python tkinter中text与Botton的问题

本人萌新
写了个一按Botton实现在text中显示余数的代码
我希望是totle=totle-var能够不断循环，显示出余数
例如我输入5，一按botton，text显示的是15，再按一下botton,显示的是10
不知道怎么改代码能够实现

import tkinter as tk
window=tk.Tk()
window.title('my window')
window.geometry('200x200')
e=tk.Entry(window,show='')
e.pack()
def insert_point():
    var=e.get() 
    var=int(var)
    totle=20
    totle=totle-var
    t.insert('insert',totle)
    var=e.get()
def delete_point():
    t.delete('1.0','end')
b1=tk.Button(window,text='收入',width=15,height=2,command=insert_point)
b1.pack()
b2=tk.Button(window,text='清除',width=15,height=2,command=delete_point)
b2.pack()
t=tk.Text(window,height=2)    
t.pack()

window.mainloop()

你好，我稍微修改了一点你的代码，希望可以帮到你。（把totle改成全局变量就好了）

import tkinter as tk

window = tk.Tk()
window.title('my window')
window.geometry('200x200')
e = tk.Entry(window, show='')
e.pack()
# totle是全局变量
totle = 20


def insert_point():
    var = e.get()
    var = int(var)
    # 声明全局变量totle
    global totle
    totle = totle-var
    t.delete('1.0', 'end')
    t.insert('insert', totle)
    var = e.get()


def delete_point():
    t.delete('1.0', 'end')


b1 = tk.Button(window, text='收入', width=15, height=2, command=insert_point)
b1.pack()
b2 = tk.Button(window, text='清除', width=15, height=2, command=delete_point)
b2.pack()
t = tk.Text(window, height=2)
t.pack()

window.mainloop()