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

[David Cournapeau]

On Sat, Mar 27, 2010 at 8:16 AM, Raymond Hettinger
<raymond.hettinger at gmail.com> wrote:
>
> On Mar 26, 2010, at 2:16 PM, Xavier Morel wrote:
>
> How about raising an exception instead of creating nans in the first place,
> except maybe within specific contexts (so that the IEEE-754 minded can get
> their nans working as they currently do)?
>
> -1
> The numeric community uses NaNs as placeholders in vectorized calculations.

But is this relevant to python itself ? In Numpy, we indeed do use and
support NaN, but we have much more control on what happens compared to
python float objects. We can control whether invalid operations raises
an exception or not, we had isnan/isfinite for a long time, and the
fact that nan != nan has never been a real problem AFAIK.

David