Is it necessary to call Tk() when writing a GUI app with Tkinter?

Wed Feb 29 19:17:09 EST 2012

On 2/29/2012 9:24 AM, Rick Johnson wrote:
> On Feb 28, 11:06 pm, John Salerno<johnj... at gmail.com> wrote:

>> However, in the Python documentation, I see this:
>>>> root = Tk()
>> app = Application(master=root)
>> app.mainloop()
>> root.destroy()

>> I tried the above and I got the following error:
>>>> Traceback (most recent call last):
>> File "C:\Users\John\Desktop\gui.py", line 12, in<module>
>> root.destroy()
>> File "C:\Python32\lib\tkinter\__init__.py", line 1714, in destroy
>> self.tk.call('destroy', self._w)
>> _tkinter.TclError: can't invoke "destroy" command: application has been destroyed
>>>> So apparently closing the window with the X button (on Windows)
 >> implicitly calls the destroy() method of the root frame.
 >> If that's the case, why does the documentation explicitly call it?
I do not know if tk has changed since the example was written or if it 
was buggy from the beginning. I opened an issue to fix it.
http://bugs.python.org/issue14163
> Most applications will have both: user destroying, and program
> destroying.

> from tkMessageBox import askyesnocancel

from tkinter.messagebox in 3.x
> class App(tk.Tk):
> def __init__(self):
> tk.Tk.__init__(self)
> self.title('Close Me -->')
> self.protocol("WM_DELETE_WINDOW", self.onDestroyWindow)
>> def onDestroyWindow(self):
> title = 'Confirm App Exit'
> msg = 'Save changes before exiting?'
> result = askyesnocancel(title, msg, default='cancel')
> if result is None:
> return
> elif result is True:
> print 'saving changes'
> elif result is False:
> print 'dont save changes'
> self.destroy()
>> if __name__ == '__main__':
> app = App()
> app.mainloop()

This works as adjusted for 3.x. I presume that a quit button or menu 
entry should also call onDestroyWindow so the effect is the same as 
clicking the outer [X] button.
I tried the same approach to fix the doc example, but unlike your class 
App(Tk), class App(Frame) does not a .protocol attribute. See the 
tracker issue for all my comments on the example.
I considered removing both the quit button and 'root.destroy' to get a 
beginning example that works properly, but as you said, having both is 
common so I would like both if the solution is not too esoteric.
-- 
Terry Jan Reedy