[Python-Dev] decimal.py: == and != comparisons involving NaNs

[Mark Dickinson]

On Mon, Nov 9, 2009 at 1:21 PM, Stefan Krah <stefan-usenet at bytereef.org> wrote:
> Antoine Pitrou <solipsis at pitrou.net> wrote:
>> (NB: interestingly, float("nan") does hash)
>
>
> I wonder if it should:
>
>>>> d = {float('nan'): 10, 0: 20}
>>>> 0 in d
> True
>>>> float('nan') in d
> False
>>>> d[float('nan')]
> Traceback (most recent call last):
>  File "<stdin>", line 1, in <module>
> KeyError: nan

That's because you're creating two different float nans.
Compare with:

Python 3.2a0 (py3k:76132M, Nov  6 2009, 14:47:39)
[GCC 4.2.1 (SUSE Linux)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> nan = float('nan')
>>> d = {nan: 10, 0: 20}
>>> nan in d
True
>>> d[nan]
10

Mark