What is the difference between root.destroy() and root.quit()?

Question

In Python using tkinter, what is the difference between root.destroy() and root.quit() when closing the root window?

Is one pr

Answer 1

The tkinter.Tk "quit" method exits the "mainloop" event-handler, and "destroy" destroys all the embedded widgets and only then exits the "mainloop". So is "destroy" the better of the two? Well, sometimes not. If "destroy" fails to destroy all the widgets for some reason, then "mainloop" is never exited and Python locks up. It can be better to just let Python shut things down in an orderly manner at the end of the script.

For example, if you embed a Matplotlib plot in a Tkinter window, that is useful because Matplotlib's own widgets are somewhat clunky to use. Unfortunately, if you then try to close the window by clicking the usual "X" in the title-bar, the window closes alright but leaves Python running. If the script had been started from a terminal, you'd have to mash Ctrl-C for a couple of minutes to get the prompt back. The reason being that the window-close event is bound to "destroy" which does not destroy the Matplotlib objects but leaves them orphaned.

The fix is to bind the window-close event to "quit" instead. But... if the script is started in a Tkinter-based IDE like IDLE, then that creates a new problem in that the window does not close because IDLE holds Tkinter running. So now "destroy" must be added after the mainloop. Finally, all is well.

Below is a minimal example of a Matplotlib plot that can be inverted with a press of a Tkinter button. Its window can be closed without problems. But if the windows-close event had been bound to "destroy" instead of "quit" then a locked-up Python process would remain.

#!/usr/bin/env python3
import tkinter as tk
from matplotlib.backends.backend_tkagg import FigureCanvasTkAgg
import matplotlib.pyplot as plt
root = tk.Tk()
data, = plt.plot([0,5,3,4,-5,3])
canvas = FigureCanvasTkAgg(plt.gcf(), master=root)
invert = lambda: (data.set_ydata(-data.get_ydata()), canvas.draw())
tk.Button(master=root, text="Invert", command=invert).pack()
canvas.get_tk_widget().pack(fill=tk.BOTH, expand=1)
root.protocol("WM_DELETE_WINDOW", root.quit)
root.mainloop()
root.destroy()

Edit: I'll add that by binding the window-close event to both methods, you can avoid adding a line after the "mainloop", should that be desirable for some reason:

root.protocol("WM_DELETE_WINDOW", lambda: (root.quit(), root.destroy()))