Re: NaN comparisons - Call For Anecdotes

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From	Ian Kelly <ian.g.kelly@gmail.com>
Date	Thu, 17 Jul 2014 14:39:42 -0600
Subject	Re: NaN comparisons - Call For Anecdotes
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On Thu, Jul 17, 2014 at 1:10 PM, Marko Rauhamaa <marko@pacujo.net> wrote:
> Mathematically, there are undefined operations, for a good reason.
> That's because the limits are not unambiguous and that's why 0/0, 0**0,
> 1/0 and inf-inf are undefined.

Well, 0**0 is usually defined as 1, despite the limits being
ambiguous.  Also, 1/0 in IEEE 754 is defined as inf.

> Why 0/0 results in an exception but inf-inf = nan, I don't see a
> justification.

I expect that float division by zero was made to raise an exception
for consistency with integer division by zero, where it might be
considered inappropriate to switch types and return inf or nan.
Granted that nowadays integer division returns a float anyway, but
there is still floor division to think about. Maybe this should have
been fixed in Python 3, but it wasn't.

Thread

Re: NaN comparisons - Call For Anecdotes "Anders J. Munch" <2014@jmunch.dk> - 2014-07-10 01:03 +0200
  Re: NaN comparisons - Call For Anecdotes Johann Hibschman <jhibschman@gmail.com> - 2014-07-17 11:12 -0400
    Re: NaN comparisons - Call For Anecdotes Chris Angelico <rosuav@gmail.com> - 2014-07-18 01:36 +1000
      Re: NaN comparisons - Call For Anecdotes Johann Hibschman <jhibschman@gmail.com> - 2014-07-17 14:49 -0400
        Re: NaN comparisons - Call For Anecdotes Chris Angelico <rosuav@gmail.com> - 2014-07-18 04:55 +1000
          Re: NaN comparisons - Call For Anecdotes Marko Rauhamaa <marko@pacujo.net> - 2014-07-17 22:10 +0300
            Re: NaN comparisons - Call For Anecdotes Ian Kelly <ian.g.kelly@gmail.com> - 2014-07-17 14:39 -0600
              Re: NaN comparisons - Call For Anecdotes Marko Rauhamaa <marko@pacujo.net> - 2014-07-18 00:08 +0300
                Re: NaN comparisons - Call For Anecdotes Ian Kelly <ian.g.kelly@gmail.com> - 2014-07-17 17:00 -0600
                Re: NaN comparisons - Call For Anecdotes Ian Kelly <ian.g.kelly@gmail.com> - 2014-07-17 17:07 -0600
        Re: NaN comparisons - Call For Anecdotes Chris Angelico <rosuav@gmail.com> - 2014-07-18 04:59 +1000
      Re: NaN comparisons - Call For Anecdotes Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2014-07-18 17:57 +0000
        Re: NaN comparisons - Call For Anecdotes Chris Angelico <rosuav@gmail.com> - 2014-07-19 05:49 +1000

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