[Python-Dev] PyObject_RichCompareBool identity shortcut

[Nick Coghlan]

On Thu, Apr 28, 2011 at 2:54 PM, Guido van Rossum <guido at python.org> wrote:
>> Well, I didn't say that. If Python changed its behavior for (float('nan') ==
>> float('nan')), we'd have to seriously consider some changes.
>
> Ah, but I'm not proposing anything of the sort! float('nan') returns a
> new object each time and two NaNs that are not the same *object* will
> still follow the IEEE std. It's just when comparing a NaN-valued
> *object* to *itself* (i.e. the *same* object) that I would consider
> following the lead of Python's collections.

The reason this possibility bothers me is that it doesn't mesh well
with the "implementations are free to cache and reuse immutable
objects" rule. Although, if the updated NaN semantics were explicit
that identity was now considered part of the value of NaN objects
(thus ruling out caching them at the implementation layer), I guess
that objection would go away.

Regards,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia