type(None)()

[Laszlo Nagy]

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()