[Python-Dev] Not-a-Number

[Mark Dickinson]

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 invalid_operation 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.non_stop_arithmetic():
        ...

But this is python-ideas territory.

Mark