[Python-Dev] Counting collisions for the win

[Barry Warsaw]

On Jan 20, 2012, at 01:50 PM, Victor Stinner wrote:

>Counting collision doesn't solve this case, but it doesn't make the
>situation worse than before. Raising quickly an exception is better
>than stalling for minutes, even if I agree than it is not the best
>behaviour.

ISTM that adding the possibility of raising a new exception on dictionary
insertion is *more* backward incompatible than changing dictionary order,
which for a very long time has been known to not be guaranteed.  You're
running some application, you upgrade Python because you apply all security
fixes, and suddenly you're starting to get exceptions in places you can't
really do anything about.  Yet those exceptions are now part of the documented
public API for dictionaries.  This is asking for trouble.  Bugs will suddenly
start appearing in that application's tracker and they will seem to the
application developer like Python just added a new public API in a security
release.

OTOH, if you change dictionary order and *that* breaks the application, then
the bugs submitted to the application's tracker will be legitimate bugs that
have to be fixed even if nothing else changed.

So I still think we should ditch the paranoia about dictionary order changing,
and fix this without counting.  A little bit of paranoia could creep back in
by disabling the hash fix by default in stable releases, but I think it would
be fine to make that a compile-time option.

-Barry