I see, I think "property" is what I'm looking for. But how would you design it yourself (you said it's a little ugly, I love to hear better ideas)? My only concern is to avoid unnecessary DB accesses (or any other expensive processes).
Thanks. On 8/16/07, Tiger12506 <[EMAIL PROTECTED]> wrote: > > > > Sorry about that. I want something like: > > > > class foo: > > > > def __init__(self): > > > > self.attr1 = None > > > > > > def get_attr1(self): > > > > if not self.attr1: > > > > attr1 = <get value from DB, very expensive query> > > > > self.attr1 = attr1 > > > > return self.attr1 > > > > > > such that: > > > > foo_instance = foo() > > > > then: > > > > foo_instance.get_attr1() > > > > and > > > > foo_instance.attr1 > > > > gets the same value. > > > > Such that you get to derive attr1 only as needed and just once, both > > outside > > and within foo class. > > > > Or is it a bad idea or just plain ugly to do something like that? If it > > is, > > kindly suggest better approach. > > > > Thanks. > > It's a little ugly but not too bad. What you are describing are > properties. > > class Foo: > def _get_attr1(self): > if not self.attr1: > attr1 = TheValue > return attr1 > def _set_attr1(self, value): > self.attr1 = value > ChangeDBFunction(value) > attr1 = property(self._get_attr1,self._setattr1,None,None) > > I think that will work. The docs seem to suggest that you should subclass > `object`. > JS > > _______________________________________________ > Tutor maillist - Tutor@python.org > http://mail.python.org/mailman/listinfo/tutor >
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