如何在root.mainloop()之后从选中的单选按钮中检索值？

import tkinter as tk

def get_selected_value():
    selected_value = radio_var.get()
    print("Selected value:", selected_value)

root = tk.Tk()

# 创建一个IntVar变量
radio_var = tk.IntVar()

# 创建单选按钮，并将variable参数设置为radio_var
radio_button1 = tk.Radiobutton(root, text="Option 1", variable=radio_var, value=1)
radio_button2 = tk.Radiobutton(root, text="Option 2", variable=radio_var, value=2)
radio_button3 = tk.Radiobutton(root, text="Option 3", variable=radio_var, value=3)

# 将单选按钮放置到窗口中
radio_button1.pack()
radio_button2.pack()
radio_button3.pack()

# 创建一个按钮，用于检索选中的单选按钮值
button = tk.Button(root, text="Get Selected Value", command=get_selected_value)
button.pack()

root.mainloop()