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Re: type(None)()

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On Thu, Aug 16, 2012 at 6:47 AM, Hans Mulder <hansmu@xs4all.nl> wrote:
> On 8/08/12 04:14:01, Steven D'Aprano wrote:
>> NoneType raises an error if you try to create a second instance. bool
>> just returns one of the two singletons (doubletons?) again.
>>
>> py> type(None)()
>> Traceback (most recent call last):
>>   File "<stdin>", line 1, in <module>
>> TypeError: cannot create 'NoneType' instances
>
> Why is that?
>
> Why doesn't it just return an existing instance of the type,
> like bool, int, str and other built-in non-mutable types do?

Because unlike those other types there is no use case for that.  It's
simpler to raise an error.

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type(None)() Hans Mulder <hansmu@xs4all.nl> - 2012-08-16 14:47 +0200
  Re: type(None)() Laszlo Nagy <gandalf@shopzeus.com> - 2012-08-16 14:54 +0200
  Re: type(None)() Chris Angelico <rosuav@gmail.com> - 2012-08-16 23:37 +1000
  Re: type(None)() Ian Kelly <ian.g.kelly@gmail.com> - 2012-08-16 07:56 -0600
  Re: type(None)() Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-08-16 13:58 +0000
    Re: type(None)() Stefan Behnel <stefan_ml@behnel.de> - 2012-08-16 17:31 +0200
    Re: type(None)() Stefan Behnel <stefan_ml@behnel.de> - 2012-08-16 17:44 +0200
    Re: type(None)() Ethan Furman <ethan@stoneleaf.us> - 2012-08-16 09:06 -0700
  Re: type(None)() Robert Kern <robert.kern@gmail.com> - 2012-08-16 15:56 +0100
  Re: type(None)() MRAB <python@mrabarnett.plus.com> - 2012-08-16 16:13 +0100
  Re: type(None)() Ethan Furman <ethan@stoneleaf.us> - 2012-08-16 09:07 -0700

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