Thanks for the reply. And I think I wasn't clear enough. I was wondering
what the metaclass `type`'s `type.__call__` does explicitly. I'm reasonably
comfortable writing metaclasses when I need them, and I understand how
`.__call__` works for non-metaclass objects.
In my first email I gave three possible ways to write a @classmethod that
returns an instance of that class. I'm not sure which one is the "most
pythonic" or "most correct", but I'm pretty sure I can get them all to
work. I'll paste them below again, and I'm wondering which one I should use
and why. Thanks!
@classmethod
def normal_constructor(cls, *args, **kwargs):
return type.__call__(*args, **kwargs)
@classmethod
def normal_constructor(cls, *args, **kwargs):
return super(???).__call__(*args, **kwargs) # I'm not sure what should
go in the super here (I'm using python3)
@classmethod
def normal_constructor(cls, *args, **kwargs):
self = cls.__new__(cls)
self.__init__(*args, **kwargs)
return self
On Wed, Nov 1, 2017 at 6:51 PM, Stefan Ram <r...@zedat.fu-berlin.de> wrote:
> Jason Maldonis <jjmaldo...@gmail.com> writes:
> >I was looking for documentation for what exactly `type.__call__` does so
> >that I can emulate it, but I wasn't able to find any docs explicitly
> >detailing what that method does. If someone knows where this info is that
> >would be great too.
>
> Instances are callable if their class has a __call__ method.
>
> When an instance is called, this __call__ method will be called.
>
> main.py
>
> class example:
> def __call__( this ):
> print( 'called' )
> instance = example()
> instance()
>
> transcript
>
> called
>
> The general contract of this method is that it can do
> whatever the author of the class deems appropriate.
>
> What exectly this is has to be documented in the
> documentation of each specific class.
>
> In fact, the attribute »instance.__call__« has a »__call__«
> attribute itself, thus:
>
> main.py
>
> class example:
> def __call__( this ):
> print( 'called' )
> instance = example()
> instance()
> instance.__call__()
> instance.__call__.__call__()
>
> transcript
>
> called
> called
> called
>
> A type also is an instance, so
>
> int.__call__(whatever)
>
> should do the same as
>
> int( whatever )
>
> . In Python 2 they had
>
> operator.isCallable( obj )
>
> , in Python 3 we can emulate this using
>
> hasattr( obj, '__call__' )
>
> .
>
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>
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