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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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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:10613

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