[Python-Dev] Issue 14417: consequences of new dict runtime error

Thu Mar 29 22:48:14 CEST 2012

On 2012年3月29日 16:31:03 -0400, "R. David Murray" <rdmurray at bitdance.com> wrote:
> On 2012年3月29日 13:09:17 -0700, Guido van Rossum <guido at python.org> wrote:
> > My original assessment was that this only affects dicts whose keys
> > have a user-implemented __hash__ or __eq__ implementation, and that
> > the number of apps that use this *and* assume the threadsafe property
> > would be pretty small. This is just intuition, I don't have hard
> > facts. But I do want to stress that not all dict lookups automatically
> > become thread-unsafe, only those that need to run user code as part of
> > the key lookup.
>> You are probably correct, but the thing is that one still has to do the
> code audit to be sure...and then make sure that no one later introduces
> such an object type as a dict key.

I just did a quick grep on our project. We are only defining __eq__
and __hash__ a couple places, but both are objects that could easily get
used as dict keys (there is a good chance that's *why* those methods are
defined) accessed by more than one thread. I haven't done the audit to
find out :)
The libraries we depend on have many more definitions of __eq__ and
__hash__, and we'd have to check them too. (Including SQLAlchemy,
and I wouldn't want that job.)
So our intuition that this is not common may be wrong.
--David