在tkinter计算器中显示减号和加号

import tkinter as tk

def add():
    result = int(entry.get()) + int(entry2.get())
    label_result.config(text=str(result))

def subtract():
    result = int(entry.get()) - int(entry2.get())
    label_result.config(text=str(result))

root = tk.Tk()

label = tk.Label(root, text="第一个数：")
label.pack()

entry = tk.Entry(root)
entry.pack()

label2 = tk.Label(root, text="第二个数：")
label2.pack()

entry2 = tk.Entry(root)
entry2.pack()

button_add = tk.Button(root, text="+", command=add)
button_add.pack()

button_subtract = tk.Button(root, text="-", command=subtract)
button_subtract.pack()

label_result = tk.Label(root, text="结果：")
label_result.pack()

root.mainloop()