super question

[Gonçalo Rodrigues]

Hi,

Ok, now I'm really confused. What is supposed

super(<class>, <subclass of class>)

to do?

My thought was that with the following setup:
[color=blue][color=green][color=darkred]
>>> class Test(object):[/color][/color][/color]
.... def test(self):
.... return "I'm %r." % self
....[color=blue][color=green][color=darkred]
>>> class Test2(Test):[/color][/color][/color]
.... def test(self):
.... return "I'm a no one."
....[color=blue][color=green][color=darkred]
>>> super(Test, Test2).test[/color][/color][/color]
Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
AttributeError: 'super' object has no attribute 'test'

So far so good, object class (the super class of Test) defines no test
method so it barfs. But
[color=blue][color=green][color=darkred]
>>> super(Test2, Test2).test[/color][/color][/color]
<bound method Test2.test of <class '__main__.Test2 '>>

Huh? shouldn't it return the *unbound* method test at class Test? And
more:
[color=blue][color=green][color=darkred]
>>> a = Test2()
>>> super(Test2, Test2).test(a)[/color][/color][/color]
Traceback (most recent call last):
File "<interacti ve input>", line 1, in ?
TypeError: test() takes exactly 1 argument (2 given)[color=blue][color=green][color=darkred]
>>> super(Test2, Test2).test()[/color][/color][/color]
"I'm <class '__main__.Test2 '>."[color=blue][color=green][color=darkred]
>>>[/color][/color][/color]

A bug? Or my perceptions on what super(<class>, <subclass of class>)
should do are totally mixed up?

With my best regards,
G. Rodrigues

[Michael Hudson]

Re: super question

Gonçalo Rodrigues <op73418@mail.t elepac.pt> writes:
[color=blue]
> Hi,
>
> Ok, now I'm really confused. What is supposed
>
> super(<class>, <subclass of class>)
>
> to do?[/color]

My *guess* (and it is very much a guess) is that super(<class>,
<subclass of class>) is intended to be used in classmethods.

Cheers,
mwh

--
Wise frogs would take sanctuary in the cool moistness of the cat's
milk-dish, from where they would watch you. It's worrying being
watched by a milk-dish. -- Tanuki the Raccoon-dog, asr

[Harry Pehkonen]

Re: super question

Sorry -- Google is not letting me reply to the correct posting . . .

Aahz wrote:[color=blue][color=green]
> > but why not just do:
> >
> > class C(B):
> > def meth(self, arg):
> > B.meth(self, arg)
> >
> >Is there any difference?
> >Any advantage either way?[/color][/color]
[color=blue]
> The advantage comes when you rename B or when you have multiple base
> classes for C.[/color]

Like this?:

class C(A, B):
def __init__(self):
for parent in C.__bases__:
parent.__init__ (self)

I don't think there is one definitive answer to the question of how to do this.

Harry.

[Terry Reedy]

Re: super question


"Harry Pehkonen" <harry.pehkonen @hotpop.com> wrote in message
news:70df36e9.0 309011030.4de74 e3b@posting.goo gle.com...[color=blue]
> Aahz wrote:[color=green][color=darkred]
> > > but why not just do:
> > >
> > > class C(B):
> > > def meth(self, arg):
> > > B.meth(self, arg)
> > >
> > >Is there any difference?
> > >Any advantage either way?[/color][/color]
>[color=green]
> > The advantage comes when you rename B or when you have multiple[/color][/color]
base[color=blue][color=green]
> > classes for C.[/color]
>
> Like this?:
>
> class C(A, B):
> def __init__(self):
> for parent in C.__bases__:
> parent.__init__ (self)[/color]

If A and B have common ancestor D, and both have code like either of
above, then above will result in two calls to D.__init__, once before
and once after B.__init__. I believe point of super mechanism is to
have D.__init__ called once at the proper time.

TJR