what exactly does type.__call__ do?

[Jason Maldonis]

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 <ram at zedat.fu-berlin.de> wrote:

> Jason Maldonis <jjmaldonis at 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__' )
>
>   .
>
> --
> https://mail.python.org/mailman/listinfo/python-list
>