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From: Ian Kelly <ian.g.kelly@gmail.com>
Date: Thu, 16 Aug 2012 07:56:03 -0600
Subject: 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.