[Python-Dev] Not-a-Number (original) (raw)

Antoine Pitrou solipsis at pitrou.net
Sat Apr 30 12:37:22 CEST 2011

On Sat, 30 Apr 2011 08:02:33 +0100 Mark Dickinson <dickinsm at gmail.com> wrote:

On Fri, Apr 29, 2011 at 2:18 AM, Greg Ewing <greg.ewing at canterbury.ac.nz> wrote: > Taking a step back from all this, why does Python allow > NaNs to arise from computations at all?

History, I think. There's a c.l.p. message from Tim Peters somewhere saying something along the lines that he'd love to make (e.g.,) 1e300 * 1e300 raise an exception instead of producing an infinity, but dare not for fear of the resulting outcry from people who use the current behaviour. Apologies if I've misrepresented what he actually said---I'm failing to find the exact message at the moment. If it weren't for backwards compatibility, I'd love to see Python raise exceptions instead of producing IEEE special values: IOW, to act as though the divide-by-zero, overflow and invalidoperation FP signals all produce an exception. As a bonus, perhaps there could be a mode that allowed 'nonstop' arithmetic, under which infinities and nans were produced as per IEEE 754: with math.nonstoparithmetic(): ... But this is python-ideas territory.

I would much prefer this idea than the idea of making NaNs non-orderable. It would break code, but at least it would break in less unexpected and annoying ways.

Regards

Antoine.

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