How to handle Invalid command name error, while executing ("after" script) in tkinter python

This error occurs when destroying the window before a callback scheduled with after is executed. To avoid this kind of issue, you can store the id returned when scheduling the callback and cancel it when destroying the window, for instance using protocol('WM_DELETE_WINDOW', quit_function).

Here is an example:

import tkinter as tkdef callback():    global after_id    var.set(var.get() + 1)    after_id = root.after(500, callback)def quit():    """Cancel all scheduled callbacks and quit."""    root.after_cancel(after_id)    root.destroy()root = tk.Tk()root.pack_propagate(False)var = tk.IntVar()tk.Label(root, textvariable=var).pack()callback()root.protocol('WM_DELETE_WINDOW', quit)root.mainloop()

Also, Tcl/Tk has an after info method which is not directly accessible through the python wrapper but can be invoked using root.tk.eval('after info') and returns a string of ids: 'id1 id2 id3'. So an alternative to keeping track of all ids is to use this:

import tkinter as tkdef callback():    var.set(var.get() + 1)    root.after(500, callback)def quit():    """Cancel all scheduled callbacks and quit."""    for after_id in root.tk.eval('after info').split():        root.after_cancel(after_id)    root.destroy()root = tk.Tk()root.pack_propagate(False)var = tk.IntVar()tk.Label(root, textvariable=var).pack()callback()root.protocol('WM_DELETE_WINDOW', quit)root.mainloop()