When setting the font in IDLE's Preferences dialog on OSX, having 
started IDLE from the command line, the font is changed and the 
following is printed:

Exception in Tkinter callback
Traceback (most recent call last):
  File 
"/Library/Frameworks/Python.framework/Versions/3.0/lib/python3.0/tkinter
/__init__.py", line 1399, in __call__
    return self.func(*args)
  File 
"/Library/Frameworks/Python.framework/Versions/3.0/lib/python3.0/idlelib
/configDialog.py", line 1125, in Ok
    self.Apply()
  File 
"/Library/Frameworks/Python.framework/Versions/3.0/lib/python3.0/idlelib
/configDialog.py", line 1129, in Apply
    self.DeactivateCurrentConfig()
  File 
"/Library/Frameworks/Python.framework/Versions/3.0/lib/python3.0/idlelib
/configDialog.py", line 1107, in DeactivateCurrentConfig
    winInstances = self.parent.instance_dict.keys()
  File 
"/Library/Frameworks/Python.framework/Versions/3.0/lib/python3.0/tkinter
/__init__.py", line 1708, in __getattr__
    return getattr(self.tk, attr)
AttributeError: 'tkapp' object has no attribute 'instance_dict'

FWIW, I am not able to reproduce this using a release3.0 IDLE (so with 
today's patches) built with the default Apple-supplied Tcl/Tk in 10.5.  
Are you using a newer Tcl/Tk?  Does it happen if you move your current 
preferences out of ~/.idlerc?

At 10:56 PM +0000 02/12/09, Ned Deily wrote:
>Ned Deily <nad@acm.org> added the comment:
>
>FWIW, I am not able to reproduce this using a release3.0 IDLE (so with
>today's patches) built with the default Apple-supplied Tcl/Tk in 10.5. 
>Are you using a newer Tcl/Tk?  Does it happen if you move your current
>preferences out of ~/.idlerc?
>

It does still happen if I move my preferences. And move my .Idle.py.
I did build it with a newer Tk -- 8.5 installed as a Framework.
(And I switched the order of /System/Library/Frameworks and /Library/Frameworks,
which makes more sense. I thought I had seen that as an Issue, but it must have been
just a web page where I saw it. Similarly, I added /opt/local/lib and /opt/local/include
in detect_modules before the directories that are added, so that it finds the readline I
installed with "port".)

So, I started again with a fresh checkout. I didn't switch the order of the Frameworks
directories, and I tried it with and without the directories for readline. I started Python
manually, imported Tk, checked it's version, etc. to confirm I was getting the Apple
installation.  If I try to run bin/idle from the 3.1 Frameworks version directory
I get a segmentation fault. I've seen a lot of weird behavior over the years in my
many configuration and installation escapades across a wide variety of software,
but I've never seen a seg fault with anything to do with Python.  I have the "do you
want to report this" backtrace if you're interested. A little later I'll try this from scratch
on a clean, though PowerPC (G4), machine and see what happens.

OK, so I built 3.1 on a clean (G4) system instead of my highly 
tangled Intel and didn't get the seg fault. I guess the issue isn't 
real.

I get the same problem when I try to change the key set.  This is on on 
intel build using Tk 8.5, and the latest 3.1 source checked out with 
bzr.  

I too changed the order of /Library/Frameworks and 
/System/Library/Frameworks in setup.py

A simple fix for me was to add the line

root.instance_dict = {}

in macosxsupport.py  That does not seem to have any other ill effects.

Added Brad's snippet to macosxSupport.py: see http://bugs.python.org/issue6075

Superceeded by 6075.