inherit without calling parent class constructor?

[Jeff Shannon]

Christian Dieterich wrote:

> On Déardaoin, Ean 27, 2005, at 14:05 America/Chicago, Jeff Shannon wrote:
>  
>> the descriptor approach does.  In either case, the calculation happens 
>> as soon as someone requests D.size ...
> 
> Agreed. The calculation happens as soon as someone requests D.size. So 
> far so good. Well, maybe I'm just not into it deep enough. As far as I 
> can tell, In your class D the calculation happens for every 
> instantiation of D, right? For my specific case, I'd like a construct 
> that calculates D.size exactly once and uses the result for all 
> subsequent instantiations.

Okay, so size (and the B object) is effectively a class attribute, 
rather than an instance attribute.  You can do this explicitly --

class D(object):
     _B = None
     def __getattr__(self, attr):
         if self._B is None:
             if myB is None:
                 myB = B()
             D._B = myB
         return getattr(self._B, attr)

Now, when the B object is first needed, it's created (triggering that 
expensive calculation) and stored in D's class object.  Since all 
instances of D share the class object, they'll all share the same 
instance of B.

Probably not worth the trouble in this particular case, but maybe in 
another case... :)

Jeff Shannon
Technician/Programmer
Credit International