Tkinter计算器如何在开始新的计算时清除过去的答案

import tkinter as tk

def clear():
    expression.set("")

def calculate():
    try:
        result = eval(expression.get())
        expression.set(str(result))
    except:
        expression.set("Error")

def button_click(value):
    current_expression = expression.get()
    if value == "C":
        clear()
    elif value == "=":
        calculate()
    else:
        expression.set(current_expression + value)

# 创建Tkinter窗口
window = tk.Tk()
window.title("Tkinter Calculator")
window.geometry("300x200")

# 创建文本框
expression = tk.StringVar()
result_label = tk.Label(window, textvariable=expression)
result_label.pack()

# 创建按钮
buttons = [
    "7", "8", "9", "/",
    "4", "5", "6", "*",
    "1", "2", "3", "-",
    "C", "0", "=", "+"
]

for i in range(4):
    for j in range(4):
        button = tk.Button(window, text=buttons[i*4+j], command=lambda value=buttons[i*4+j]: button_click(value))
        button.grid(row=i+1, column=j, padx=5, pady=5)

# 运行Tkinter主循环
window.mainloop()