On Tue, Mar 6, 2012 at 8:56 AM, Mark Shannon <report@bugs.python.org> wrote:
>
> Mark Shannon <mark@hotpy.org> added the comment:
>
> Jim Jewett wrote:
>> Jim Jewett <jimjjewett@gmail.com> added the comment:
>>
>> Can't this be triggered by non-malicious code that just happened to have a python comparison and get hit with a thread switch?
>
> So, they are writing to a dict in one thread while reading from the same
> dict in another thread, without any external locks and with keys written
> in Python.
>>
>> I'm not sure how often it happens, but today it would not be visible to the user; after the patch, users will see a sporadic failure that they can't easily defend against.
>>
> I suspect, they are already seeing sporadic failures.
> I think raising an exception is better than weird failures.
>
> We should document the new behaviour, as it is a change in semantics.

+1 on everything you said.