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Groups > comp.lang.python > #6558

Re: float("nan") in set or as key

From Christian Heimes <lists@cheimes.de>
Subject Re: float("nan") in set or as key
Date 2011-05-29 20:05 +0200
References (1 earlier) <mailman.2207.1306628936.9059.python-list@python.org> <irsarj$2b9$1@reader1.panix.com> <mailman.2215.1306657864.9059.python-list@python.org> <irtlu8$qk3$1@reader1.panix.com> <4DE285E8.4080801@mrabarnett.plus.com>
Newsgroups comp.lang.python
Message-ID <mailman.2232.1306692322.9059.python-list@python.org> (permalink)

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Am 29.05.2011 19:44, schrieb MRAB:
> Would there be any advantage to making NaN a singleton? I'm thinking
> that it could make checking for it cheaper in the implementation of
> sets and dicts. Or making NaN unhashable?

It can't be a singleton, because IEEE 754 specifies millions of millions
of different NaN values. There are positive and negative NaNs, quiet
NaNs and signaling NaNs. 50 of 52 mantissa bits can vary freely, one bit
makes the difference between signaling and quiet NaNs and at least one
bit must be non-zero.

Christian

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Thread

Re: float("nan") in set or as key Albert Hopkins <marduk@letterboxes.org> - 2011-05-28 20:28 -0400
  Re: float("nan") in set or as key Erik Max Francis <max@alcyone.com> - 2011-05-28 17:44 -0700
  Re: float("nan") in set or as key Grant Edwards <invalid@invalid.invalid> - 2011-05-29 02:25 +0000
    Re: float("nan") in set or as key Wolfgang Rohdewald <wolfgang@rohdewald.de> - 2011-05-29 10:27 +0200
      Re: float("nan") in set or as key Grant Edwards <invalid@invalid.invalid> - 2011-05-29 14:41 +0000
        Re: float("nan") in set or as key MRAB <python@mrabarnett.plus.com> - 2011-05-29 18:44 +0100
          Re: float("nan") in set or as key Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-29 18:27 +0000
        Re: float("nan") in set or as key Chris Angelico <rosuav@gmail.com> - 2011-05-30 03:50 +1000
        Re: float("nan") in set or as key Christian Heimes <lists@cheimes.de> - 2011-05-29 20:05 +0200
          Re: float("nan") in set or as key Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-29 18:46 +0000
        Re: float("nan") in set or as key Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2011-05-29 20:36 -0700

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