Question

When the user presses a close Button that I created, some tasks are performed before exiting. However, if the user clicks on the [X] button in the top-right of the window to close the window, I cannot perform these tasks.

How can I override what happens when the user clicks [X] button?

Answer 1

It sounds as if your save window should be modal.

If this is a basic save window, why are you reinventing the wheel?
Tk has a tkFileDialog for this purpose.

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If what you want is to override the default behaviour of destroying the window, you can simply do:

root.protocol('WM_DELETE_WINDOW', doSomething)  # root is your root window

def doSomething():
    # check if saving
    # if not:
    root.destroy()

This way, you can intercept the destroy() call when someone closes the window (by any means) and do what you like.