This only seems to be a problem under Windows.
From a Portable Python discussion:
I am using Portable Python 1.1, python 3.0.1.
I am trying to set up a .bat file file to easily start IDLE. But IDLE
is throwing an error and failing some of the time.
It only happens if IDLE is set up to start in the edit mode. (Which I
prefer.) And then it only throws the error the first time a file is
opened. It doesn't seem to matter what kind of file is opened. The
other symptom is that a new line is inserted at the top of the file
that is opened.

The error is (I'm typing it by hand):
Exception in Tkinter callback
Traceback (most recent call last):
 File "E:\py30\App\lib\tkinter\__init__.py", line 1399, in __call__
   return self.func(*args)
 File "E:\py30\App\lib\idlelib\MultiCall.py", line 174, in handler
doafterhandler.pop()()
 File "E:\py30\App\lib\idlelib\MultiCall.py", line 221, in <lambda>
doit = lambda: self.bindedfuncs[triplet[2]][triplet[0]].remove(func)
ValueError: list.remove(x): x not in list

I can work around this with a batch file that uses python.exe, not
pythonw.exe, but it leaves an annoying command shell window open.

I also tested IDLE under a normal python installation and the same thing happens, so, sorry, it is not a PP thing. There must be a bug in IDLE under py 3.0. I'll file this with python.org.

I can consistently reproduce this with Python 3.0.1 by setting IDLE to start in editing mode and using Ctrl+o to open the Open dialog. Doesn't happen when using the menu item in the File menu.

This leads me to believe it has something to do with keypress event processing. Also, the event for which the unbind call is failing is <Control-KeyPress-slash>.

Continuing to investigate.

Putting print statements in that part of the world shows that the reason why the list.remove fails is that while a ColorDelegator.toggle_colorize_event object is in the list, it has a different memory address than the ColorDelegator.toggle_colorize_event object to be removed. I've seen this NOT fail occasionally (the memory addresses were the same, so the list.remove succeeded), all of which would seem to imply that something has moved in memory.

I'll mention that when the failure occurs, the list always has just one object, a ColorDelegator.toggle_colorize_event object.

Attached is a patch to fix the bug.

When selecting "Open" from the File Menu, "ishanderrunning" is empty. Unbind/Bind requests are handled synchronously.

When pressing "Ctrl+O", "ishandlerrunning" is no longer empty, and the actual bind/unbind events get appended to "doafterhandle".

The original code was running these bind/unbind events in REVERSE order by using "pop", so unbind requests were being made (and causing the error) before the proper bind request.

Brett C. just today pushed
http://hg.python.org/cpython/rev/556b9bafdee8
changeset: 76310:556b9bafdee8
user: Brett Cannon <brett@python.org>
date: Sat Apr 14 20:44:23 2012 -0400
summary:
IDLE was relying on implicit relative imports which have gone away in
Python 3.3 thanks to importlib finishing the work in PEP-328 that
accidently got carried forward.

I don't know if this patch will have any affect on this issue, but implicit relative imports are (were;-) a possible cause of intermittent problems.

Implicit relative imports are not related to this issue.

Can someone please review the given patch?

With 3.2.3, after selecting open edit on startup and using ^O to select a file, I got a silent close of the editor window. Opening from the file menu worked. After the change of adding '0', ^O worked also.

However, without a test suite, I am a little nervous about the change, as the original code might be intentional. From the module doc string:

"The order by which events are called is defined by these rules:

1. A more-specific event will be called before a less-specific event.
2. A recently-binded event will be called before a previously-binded event, unless this conflicts with the first rule."

Is popping from the end the implementation of rule 2?
Is it possible that one event pair is being appended in the wrong order?
I need to read more of the comments and code to understand this subsystem.

Code note 1: doafterhandler = self.doafterhandler (initially [] by default), so changes to the list must be mutations to affect the self attribute.

while doafterhandler:
    doafterhandler.pop(0)()
# is O(n*2)

doafterhandler.reverse()
while doafterhandler:
  doafterhandler.pop()()
# is O(n)

for f in doafterhandler:
    f()
doafterhandler[:] = []
# doafterhandler.clear() works in 3.3
# is also O(n) and replaces repeated .pop with one clear

If calling first to last is proper, I prefer this last unless the callback functions somehow require that they be removed from doafterhandler before being called.

Code note 2: unless the default args for handler

    def __create_handler(self, lists, mc_type, mc_state):
        def handler(event, lists = lists,
                    mc_type = mc_type, mc_state = mc_state,
                    ishandlerrunning = self.ishandlerrunning,
                    doafterhandler = self.doafterhandler):

are ever replaced with other arguments in handler(event) calls, their presence in the signature would appear to be holdovers from before closures. If so, the above could be simplified to
def handler(event)
and 'self.' added in the body where needed.

I also wonder whether the double underscore and consequent name mangling for __create_handler is needed. My understanding is that this is only needed, perhaps, for multiple inheritance mixin classes, and I do not see that class _ComplexBinder qualifies.

Thanks for your review, Terry.

Popping from the end is not an implementation of rule 2. Calling event handlers is separate concept from binding/unbinding event handlers. The "doafterhandler" list contains bind/unbind requests that were made while calling event handlers. The doafterhandler "queue" should be FIFO, not LIFO.

Code note 1:

The running time of the algorithm is an important consideration. Your last suggestion for using a for-loop looks most appropriate, as you've said. Attached is a revised patch for it.

Code note 2:

The _ComplexBinder class may need refactoring, but that's a separate issue. I'm willing to review patches for that.

I am seeing this as well. It does not repro 100% of the time, but frequently enough that its hard to get anything done. My repro is a little simpler and might help understanding the fix.

Win7
Python 3.3

I start IDLE normally from the shortcut in the install.
Ctrl-N to open and edit window.
Ctrl-O to open a file.
Select file and then Idle exits.

As mentioned, using the menu to open the file seems to work more reliably. I've not had a crash that way.

For what it's worth (maybe not much?), the version of IDLE produced by
Guilherme Polo in the 2009 Google Summer of Code, which VPython (vpython.org)
uses under the name VIDLE, does not have any problem with starting with an
edit window and in fact I always use it that way.

Bruce Sherwood

On Mon, Feb 4, 2013 at 8:53 PM, Patrick <report@bugs.python.org> wrote:

Patrick added the comment:

I am seeing this as well. It does not repro 100% of the time, but
frequently enough that its hard to get anything done. My repro is a little
simpler and might help understanding the fix.

Win7
Python 3.3

I start IDLE normally from the shortcut in the install.
Ctrl-N to open and edit window.
Ctrl-O to open a file.
Select file and then Idle exits.

As mentioned, using the menu to open the file seems to work more reliably.
I've not had a crash that way.

----------
nosy: +Patrick.Walters

---

Python tracker <report@bugs.python.org>
<http://bugs.python.org/issue8900\>

---

I changed the title to better reflect the original bug report.

@bruce: I did review Guilherme's patch a while ago in bpo-10079. The editor window bug can be found in bpo-6698. These are on my todo-list, especially now that PEP-434 has been accepted.

New changeset 37352a3ccd54 by Roger Serwy in branch '2.7':
bpo-8900: Using keyboard shortcuts in IDLE to open a file no longer raises an exception.
http://hg.python.org/cpython/rev/37352a3ccd54

New changeset 61092bbd1464 by Roger Serwy in branch '3.3':
bpo-8900: Using keyboard shortcuts in IDLE to open a file no longer raises an exception.
http://hg.python.org/cpython/rev/61092bbd1464

New changeset 6ad256175971 by Roger Serwy in branch 'default':
bpo-8900: merge with 3.3.
http://hg.python.org/cpython/rev/6ad256175971

I am closing this issue as being fixed.