[Python-Dev] set iteration order

[Antoine Pitrou]

On Sat, 26 Feb 2011 10:09:33 +0100
Hagen Fürstenau <hagen at zhuliguan.net> wrote:
> 
> I just hunted down a change in behaviour between Python 3.1 and 3.2 to
> possibly changed iteration order of sets due to the optimization in
> issue #8685. Of course, this order shouldn't be relied on in the first
> place, but the side effect of the optimization might be worth mentioning
> in "What's new", maybe also pointing out that the old behaviour can be
> simulated with {x for x in a if x not in b} in place of "a-b".

I'm against such a mention. It would give the impression that we
support some semblance of reproduceability in iteration order, which is
not true. If you use sets or dicts, you must deal with the fact that
the iteration order will be totally random from your (the programmer's)
POV.

Regards

Antoine.