[PythonLabs] Re: [Python-Dev] Re: [Python-checkins]python/dist/src/Modules gcmodule.c,2.33.6.5,2.33.6.6 (original) (raw)

Tim Peters tim_one@email.msn.com
Sun, 6 Apr 2003 21:11:10 -0400

[Jim Fulton]

If I understand the problem, it can be avoided by avoiding old-style classes.

In Python 2.3, that appears to be true. In Python 2.2.2, not true. The problems are caused by getattr hooks that resurrect unreachable objects, and/or remove the last reference to an unreachable object, when such a hook is on an instance reachable only from an unreachable cycle, and the class doesn't explicitly define a del method, and the class has a getattr hook, and the getattr hook does extreme things instead of just saying "no, there's no del here".

Python 2.3 introduced new machinery for new-style classes specifically aimed at answering the "does it support del?" question without invoking getattr hooks, and that's why it's not a problem for new-style classes in 2.3. New-style classes still go thru getattr hooks to answer this question in 2.2.2.

There were problem in Python and problems in Zope here. Jeremy fixed the Zope problems under 2.2 by breaking the

and the getattr hook does extreme things instead of just saying "no,
there's no __del__ here"

link of the chain for persistent objects.

Maybe it's time to, at least optionally, cause a warning when old-style classes are used. :) I'm not kidding for Zope. I think it might be worth-while to be issue such a warning in Zope.

There may be good reasons for wanting that, but none raised in this thread so far are relevant (unless 2.3 is mandated for Zope, which I'm sure we don't want to do).