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Is nan in (nan,) correct?

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Subject Is nan in (nan,) correct?
Date Thu, 05 Mar 2015 17:26:53 -0500
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It's been brought up on Stack Overflow that the "in" operator (on
tuples, and by my testing on dict and list, as well as dict lookup) uses
object identity as a shortcut, and returns true immediately if the
object being tested *is* an element of the container. However, the
contains operation does not specify whether object identity or equality
is to be used. In effect, the built-in container types use a hybrid
test: "a is b or a == b".

My question is, is this a *correct* implementation of the operator, or
are objects "supposed to" use a basis of equality for these tests?

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Is nan in (nan,) correct? random832@fastmail.us - 2015-03-05 17:26 -0500
  Re: Is nan in (nan,) correct? sohcahtoa82@gmail.com - 2015-03-05 15:11 -0800
    Re: Is nan in (nan,) correct? Ben Finney <ben+python@benfinney.id.au> - 2015-03-06 10:20 +1100
      Re: Is nan in (nan,) correct? sohcahtoa82@gmail.com - 2015-03-05 15:27 -0800
        Re: Is nan in (nan,) correct? Ben Finney <ben+python@benfinney.id.au> - 2015-03-06 10:39 +1100
        Re: Is nan in (nan,) correct? Chris Angelico <rosuav@gmail.com> - 2015-03-06 10:40 +1100
    Re: Is nan in (nan,) correct? Chris Angelico <rosuav@gmail.com> - 2015-03-06 10:25 +1100
  Re: Is nan in (nan,) correct? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-03-06 13:09 +1100
    Re: Is nan in (nan,) correct? Ben Finney <ben+python@benfinney.id.au> - 2015-03-06 13:55 +1100
    Re: Is nan in (nan,) correct? Ethan Furman <ethan@stoneleaf.us> - 2015-03-05 19:18 -0800
    Re: Is nan in (nan,) correct? Ben Finney <ben+python@benfinney.id.au> - 2015-03-06 14:26 +1100
    Re: Is nan in (nan,) correct? Ethan Furman <ethan@stoneleaf.us> - 2015-03-05 19:44 -0800
    Re: Is nan in (nan,) correct? Chris Angelico <rosuav@gmail.com> - 2015-03-06 14:49 +1100
    Re: Is nan in (nan,) correct? random832@fastmail.us - 2015-03-05 23:37 -0500
      Re: Is nan in (nan,) correct? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-03-07 04:07 +1100
    Re: Is nan in (nan,) correct? Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-03-06 04:46 +0000
  Re: Is nan in (nan,) correct? Rustom Mody <rustompmody@gmail.com> - 2015-03-06 01:50 -0800
    Re: Is nan in (nan,) correct? Chris Angelico <rosuav@gmail.com> - 2015-03-06 21:01 +1100
      Re: Is nan in (nan,) correct? Rustom Mody <rustompmody@gmail.com> - 2015-03-06 02:22 -0800
        Re: Is nan in (nan,) correct? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-03-07 03:59 +1100
          Re: Is nan in (nan,) correct? Rustom Mody <rustompmody@gmail.com> - 2015-03-06 10:04 -0800
            Re: Is nan in (nan,) correct? Ethan Furman <ethan@stoneleaf.us> - 2015-03-06 10:16 -0800
      Re: Is nan in (nan,) correct? Grant Edwards <invalid@invalid.invalid> - 2015-03-06 15:34 +0000
    Re: Is nan in (nan,) correct? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-03-07 03:43 +1100
      Re: Is nan in (nan,) correct? Rustom Mody <rustompmody@gmail.com> - 2015-03-06 09:04 -0800
        Re: Is nan in (nan,) correct? Chris Angelico <rosuav@gmail.com> - 2015-03-07 04:16 +1100
          Re: Is nan in (nan,) correct? Rustom Mody <rustompmody@gmail.com> - 2015-03-06 09:36 -0800
        Re: Is nan in (nan,) correct? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-03-07 10:33 +1100
          Re: Is nan in (nan,) correct? Rustom Mody <rustompmody@gmail.com> - 2015-03-06 18:37 -0800

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