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Re: NoneType and new instances

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From Terry Reedy <tjreedy@udel.edu>
Subject Re: NoneType and new instances
Date Sat, 30 Jul 2011 23:34:11 -0400
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On 7/30/2011 12:39 PM, bruno.desthuilliers@gmail.com wrote:
> On 28 juil, 17:39, Ethan Furman<et...@stoneleaf.us>  wrote:
>>
>> -->  bool(0) is bool(0)
>> True

> This test is not reliable

It is in the sense that it will always work -- because False/True are 
doubletone constants and so documented.

But expr is expr == True does not reliably say it will always be true, 
because

 > - a same id can be reused for terms (I have
> already seen such things happening). If you want a reliable test, use:
>
> #>  a = bool(0)
> #>  b = bool(0)
> #>  a is b
> True
>
> Note that this still fails to prove anything since bool is a subclass
> of int and CPython caches "small" integers:
>
> #>  a = 42
> #>  b = 42
> #>  a is b
> True

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Thread

NoneType and new instances Ethan Furman <ethan@stoneleaf.us> - 2011-07-28 08:39 -0700
  Re: NoneType and new instances Billy Mays <81282ed9a88799d21e77957df2d84bd6514d9af6@myhashismyemail.com> - 2011-07-28 11:34 -0400
  Re: NoneType and new instances Ben Finney <ben+python@benfinney.id.au> - 2011-07-29 07:46 +1000
    Re: NoneType and new instances Ethan Furman <ethan@stoneleaf.us> - 2011-07-28 15:26 -0700
      Re: NoneType and new instances Ben Finney <ben+python@benfinney.id.au> - 2011-07-29 09:52 +1000
  Re: NoneType and new instances Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-07-29 11:16 +1000
    Re: NoneType and new instances Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-07-30 14:50 +1200
      Re: NoneType and new instances Terry Reedy <tjreedy@udel.edu> - 2011-07-30 09:35 -0400
      Re: NoneType and new instances python@bdurham.com - 2011-07-30 11:43 -0400
  Re: NoneType and new instances "bruno.desthuilliers@gmail.com" <bruno.desthuilliers@gmail.com> - 2011-07-30 09:39 -0700
    Re: NoneType and new instances Terry Reedy <tjreedy@udel.edu> - 2011-07-30 23:34 -0400
      Re: NoneType and new instances Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-07-31 14:28 +1000

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