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

Raymond Hettinger raymond.hettinger at gmail.com
Sat Mar 27 00:16:36 CET 2010

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)?


The numeric community uses NaNs as placeholders in vectorized calculations.
People do use them and there's no point in breaking their code.

Of the ideas I've seen in this thread, only two look reasonable:

* Do nothing.  This is attractive because it doesn't break anything.

* Have float.__eq__(x, y) return True whenever x and y are
   the same NaN object.  This is attractive because it is a
   minimal change that provides a little protection for 
   simple containers.

I support either of those options.

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