I would rather leave this open for the moment as an information resource.  I wrote query.py with a base class and subclasses to standardize asking users for input.  So some of the patch may be obsolete, but it does have a catalog of popup uses.

The patch consistently replaces tkMessagebox.showerror with widget.showerror.  I have done that in several places, although widget.showerror may just be messagebox.showerror.  At least some of my motivation was making testing easier, by adding a mock to the test instance instead of temporarily monkeypatching messagebox.  If a custom Showerror class were defined in, for instant, query.py, "self.showerror = tkMessagebox.showerror" could easily be replaced by "self.showerror = query.Showerror.

I also have some interest in consistently handling focus in response to key presses.  (There was recently a request for this on idle-dev.)