[Python-Dev] Why is nan != nan?

[Raymond Hettinger]

On Mar 25, 2010, at 4:21 PM, Georg Brandl wrote:

> Am 25.03.2010 22:45, schrieb Greg Ewing:
>> Georg Brandl wrote:
>>> Thinking of each value created by float('nan') as
>>> a different nan makes sense to my naive mind, and it also explains
>>> nicely the behavior present right now.
>> 
>> Not entirely:
>> 
>>   x = float('NaN')
>>   y = x
>>   if x == y:
>>     ...
>> 
>> There it's hard to argue that the NaNs being compared
>> result from different operations.
>> 
>> It does suggest a potential compromise, though: a single
>> NaN object compares equal to itself, but different NaN
>> objects are never equal (more or less what dict membership
>> testing does now, but extended to all == comparisons).
>> 
>> Whether that's a *sane* compromise I'm not sure.
> 
> FWIW, I like it.
> 
> Georg
> 

+1

Raymond