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Date: Thu, 16 Aug 2012 14:54:03 +0200
From: Laszlo Nagy <gandalf@shopzeus.com>
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Subject: Re: type(None)()
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On 2012-08-16 14:47, Hans Mulder 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?
Because None is a singleton. It is the only instance of its class. This 
is very useful because it allows you to write conditions like this:

if obj is None:
     do_something()