如何检测子窗口在tkinter中是打开还是关闭

import tkinter as tk

def open_window():
    global child_window
    child_window = tk.Toplevel(root)
    child_window.protocol("WM_DELETE_WINDOW", close_window)
    child_window.state = "open"

def close_window():
    child_window.state = "closed"
    child_window.destroy()

root = tk.Tk()
child_window = None

open_button = tk.Button(root, text="Open Window", command=open_window)
open_button.pack()

root.mainloop()

if child_window.state == "open":
    print("子窗口已打开")
else:
    print("子窗口已关闭")