[Zope-dev] __getattr__ and Acquisition

[Florent Guillaume]

On Mon, 2002-09-23 at 19:04, Johan Carlsson [Torped] wrote:
> At 16:29 2002-09-23 +0000, Florent Guillaume said:
> >You didn't look a the code I pointed to you. Look at CMFCore/Skinnable
> >to be precise (not everything is to be used of course).
> >
> >* In __of__ you store the parent in a volatile attribute,
> >* in __getattr__ you lookup the volatile attribute
> >
> >This works as long as your object is not used in several different
> >acquisition contexts.
> 
> Hi Florent,
> Would you care to elaborate on that last sentence? :-)
> Could you give an example when it wouldn't work?

Sure.

If your object with special __of__ and __getattr__ is o and you do
x = f.o
     #  o.__of__(f) is called so f is stored in o._v_stuff
y = f.g.o
     #  o.__of__(f.g) is called so f.g is stored in o._v_stuff
x['foo']
     # o's __getattr__ finds f.g stored in _v_stuff and not f.

But it's not necessarily a problem if you take care to use aq_inner.
That depends on the use you have for the parent, really.

Florent


-- 
Florent Guillaume, Nuxeo (Paris, France)
+33 1 40 33 79 87  http://nuxeo.com  mailto:fg@nuxeo.com