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
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