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Groups > comp.lang.python > #6827
| From | Grant Edwards <invalid@invalid.invalid> |
|---|---|
| Newsgroups | comp.lang.python |
| Subject | Re: float("nan") in set or as key |
| Date | 2011-06-01 21:01 +0000 |
| Organization | PANIX Public Access Internet and UNIX, NYC |
| Message-ID | <is69b3$pnc$1@reader1.panix.com> (permalink) |
| References | <mailman.2206.1306626083.9059.python-list@python.org> <94dkd3F7k4U1@mid.individual.net> <4de1e3e7$0$2195$742ec2ed@news.sonic.net> <4de22007$0$29996$c3e8da3$5496439d@news.astraweb.com> <pan.2011.05.29.21.19.12.375000@nowhere.com> |
On 2011-05-29, Nobody <nobody@nowhere.com> wrote:
> On Sun, 29 May 2011 10:29:28 +0000, Steven D'Aprano wrote:
>
>>> The correct answer to "nan == nan" is to raise an exception, because
>>> you have asked a question for which the answer is nether True nor
>>> False.
>>
>> Wrong.
>
> That's overstating it. There's a good argument to be made for raising
> an exception. Bear in mind that an exception is not necessarily an
> error, just an "exceptional" condition.
>
>> The correct answer to "nan == nan" is False, they are not equal.
>
> There is no correct answer to "nan == nan".
For those of us who have to deal with the real world (that means
complying with IEEE-754), there _is_ a correct answer. IIRC, the IEEE
standard requires nan == nan is false, and nan != nan is true.
That said, I don't remember what the other comparisons are supposed to
do...
> Defining it to be false is just the "least wrong" answer.
>
> Arguably, "nan != nan" should also be false, but that would violate
> the invariant "(x != y) == !(x == y)".
And it would violate the IEEE standard. IEEE-754 has it's warts, but
we're far better off than we were with dozens of incompatible,
undocumented, vendor-specific schemes (most of which had more warts
than IEEE-754).
--
Grant Edwards grant.b.edwards Yow! I'm dressing up in
at an ill-fitting IVY-LEAGUE
gmail.com SUIT!! Too late...
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float("nan") in set or as key MRAB <python@mrabarnett.plus.com> - 2011-05-29 00:41 +0100
Re: float("nan") in set or as key Erik Max Francis <max@alcyone.com> - 2011-05-28 17:16 -0700
Re: float("nan") in set or as key Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-29 00:26 +0000
Re: float("nan") in set or as key Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-29 13:04 +1200
Re: float("nan") in set or as key John Nagle <nagle@animats.com> - 2011-05-28 23:12 -0700
Re: float("nan") in set or as key Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-29 10:29 +0000
Re: float("nan") in set or as key Nobody <nobody@nowhere.com> - 2011-05-29 22:19 +0100
Re: float("nan") in set or as key Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-29 23:31 +0000
Re: float("nan") in set or as key Nobody <nobody@nowhere.com> - 2011-06-01 21:41 +0100
Re: float("nan") in set or as key Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-02 09:54 +0000
Re: float("nan") in set or as key Grant Edwards <invalid@invalid.invalid> - 2011-06-02 13:05 +0000
Re: float("nan") in set or as key Robert Kern <robert.kern@gmail.com> - 2011-06-02 12:04 -0500
Re: float("nan") in set or as key Nobody <nobody@nowhere.com> - 2011-06-02 21:47 +0100
Re: float("nan") in set or as key Grant Edwards <invalid@invalid.invalid> - 2011-06-03 14:52 +0000
Re: float("nan") in set or as key Chris Torek <nospam@torek.net> - 2011-06-03 17:52 +0000
Re: float("nan") in set or as key Grant Edwards <invalid@invalid.invalid> - 2011-06-06 13:54 +0000
Re: float("nan") in set or as key Nobody <nobody@nowhere.com> - 2011-06-04 00:29 +0100
Re: float("nan") in set or as key Chris Angelico <rosuav@gmail.com> - 2011-06-04 09:51 +1000
Re: float("nan") in set or as key rusi <rustompmody@gmail.com> - 2011-06-04 00:52 -0700
Re: float("nan") in set or as key Nobody <nobody@nowhere.com> - 2011-06-04 20:29 +0100
Re: float("nan") in set or as key Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-05 07:21 +0000
Re: float("nan") in set or as key Nobody <nobody@nowhere.com> - 2011-06-05 19:15 +0100
Re: float("nan") in set or as key Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-06 00:55 +0000
Re: float("nan") in set or as key Nobody <nobody@nowhere.com> - 2011-06-06 23:14 +0100
Re: float("nan") in set or as key Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-06 23:44 +0000
Re: float("nan") in set or as key Chris Angelico <rosuav@gmail.com> - 2011-06-07 11:00 +1000
Re: float("nan") in set or as key Grant Edwards <invalid@invalid.invalid> - 2011-06-06 14:03 +0000
Re: float("nan") in set or as key Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-06-03 11:17 +1200
Re: float("nan") in set or as key Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-03 04:23 +0000
Re: float("nan") in set or as key Chris Angelico <rosuav@gmail.com> - 2011-06-03 14:35 +1000
Re: float("nan") in set or as key Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-03 05:59 +0000
Re: float("nan") in set or as key Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-06-04 12:14 +1200
Re: float("nan") in set or as key Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-06-04 02:21 +0000
Re: float("nan") in set or as key Erik Max Francis <max@alcyone.com> - 2011-06-05 00:27 -0700
Re: float("nan") in set or as key Grant Edwards <invalid@invalid.invalid> - 2011-06-01 21:01 +0000
Re: float("nan") in set or as key Chris Torek <nospam@torek.net> - 2011-05-30 00:02 +0000
Re: float("nan") in set or as key Raymond Hettinger <python@rcn.com> - 2011-05-29 21:49 -0700
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