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Groups > comp.lang.python > #6499
| Date | 2011-05-28 17:16 -0700 |
|---|---|
| From | Erik Max Francis <max@alcyone.com> |
| Organization | Alcyone Systems |
| Newsgroups | comp.lang.python |
| Subject | Re: float("nan") in set or as key |
| References | <mailman.2206.1306626083.9059.python-list@python.org> |
| Message-ID | <O6GdnSCKr8XvDXzQnZ2dnUVZ5r6dnZ2d@giganews.com> (permalink) |
MRAB wrote:
> Here's a curiosity. float("nan") can occur multiple times in a set or as
> a key in a dict:
>
> >>> {float("nan"), float("nan")}
> {nan, nan}
>
> except that sometimes it can't:
>
> >>> nan = float("nan")
> >>> {nan, nan}
> {nan}
It's fundamentally because NaN is not equal to itself, by design.
Dictionaries and sets rely on equality to test for uniqueness of keys or
elements.
>>> nan = float("nan")
>>> nan == nan
False
In short, don't do that.
--
Erik Max Francis && max@alcyone.com && http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM/Y!M/Skype erikmaxfrancis
There was never a good war or a bad peace.
-- Benjamin Franklin, 1706-1790
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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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