Basic misunderstanding on object creation

[andrew cooke]

On Wednesday, 13 May 2015 11:56:21 UTC-3, Ian  wrote:
> On Wed, May 13, 2015 at 8:45 AM, andrew cooke <andrew at acooke.org> wrote:
> >>>> class Foo:
> > ...     def __new__(cls, *args, **kargs):
> > ...         print('new', args, kargs)
> > ...         super().__new__(cls)
> > ...
> >>>> class Bar(Foo):
> > ...     def __init__(self, a):
> > ...         print('init', a)
> > ...
> >>>> Bar(1)
> > new (1,) {}
> >
> > no "init" is printed.
> 
> You're not returning anything from Foo.__new__, so the result of the
> constructor is None.  None.__init__ does nothing.

ah, you're right, thanks.  that was a typo.


more generally, it seems that the error is:

  (1) __new__ is called and then __init__ from some other, external code

  (2) in 3.2 anything passed to object's __new__ was silently discarded.

the following code works in 3.2 and 3.4:

class Foo:
    def __new__(cls, *args, **kargs):
        print("new", args, kargs)
        return super().__new__(cls)

class Bar(Foo): 
    def __init__(self, *args, **kargs):
        print("init", args, kargs)

Bar(1)

(while my original code didn't).

thanks everyone,
andrew