<p>How do I handle the window close event (user clicking the 'X' button) in a Python Tkinter program?</p>

Tkinter supports a mechanism called
protocol handlers
. Here, the term
protocol
refers to the interaction between the application and the window manager. The most commonly used protocol is called
```
WM_DELETE_WINDOW
```
, and is used to define what happens when the user explicitly closes a window using the window manager.
You can use the
```
protocol
```
method to
install a handler
for this protocol (the widget must be a
```
Tk
```
or
```
Toplevel
```
widget):
Here you have a concrete example:
```
```
import tkinter as tk
from tkinter import messagebox

root = tk.Tk()

def on_closing():
    if messagebox.askokcancel("Quit", "Do you want to quit?"):
        root.destroy()

root.protocol("WM_DELETE_WINDOW", on_closing)
root.mainloop()
```
```