[Python-Dev] Garbage collecting closures
Mon, 14 Apr 2003 18:15:58 -0400
> But I'm not sure where I would have learned to do so. The documentation
> for __del__ is out of date.
> * http://www.python.org/doc/2.3a2/ref/customization.html
> The documentation lists a variety of reasons that __del__ might not get
> called (it doesn't claim to be exhaustive but it does list some cases
> that I consider pretty obscure). It doesn't list nested recursive
__del__ isn't relevant to your test case, though: if the cycles in question
contained any object with a __del__ method, gc would never have reclaimed
them (and gc.collect() would have had no effect on them either, other than
to move the trash cycles into gc.garbage).
You had __del__-free cycles, and then there is indeed no way to predict when
they'll get reclaimed. I think that's just life; you wouldn't be any better
off in Java or Scheme or anything else.
It's always been difficult to guess when the implementation of a thing may
involve a cycle under the covers, and closures, generators and new-style
classes have created many new opportunities for cycles to appear. I don't
expect users to know when they're going to happen! I can't keep them all
straight myself. I try to write code that doesn't care, though (avoid
__del__ methods; avoid "hiding" critical resources in side effects of what
look like simple expressions; arrange for subsystems that can be explicitly
told to release critical resources). Ain't always easy.