[Python-Dev] PEP 342/343 status?

[Guido van Rossum]

[Guido]
> >uncertainty of the possibility to call close() from the
> >destructor may have slowed that down.

[Phillip]
> If you're talking about the bit about __del__ not working when hanging off
> a cycle, my apologies for creating that confusion, I misunderstood Tim's post.

No, I'm not talking about that.

> If you're talking about the circular reference scenario involving
> exceptions, then I think I've already given a tentative explanation why
> such a cycle will not include the generator-iterator itself (only its
> frame) as long as the generator-iterator clears its frame's f_back when the
> frame is not in use.  It would probably be a good idea to verify this, but
> I think the basic idea is sound.

Yes, the generator does clear its f_back when it's suspended.

> The only scenario in which a generator-iterator would be uncollectable is
> if you took some action outside the iterator to pass it into itself, or if
> you stored the iterator in a global variable.  However, even in the latter
> case, the phase of Python shutdown that clears module contents would break
> the cycle and cause the generator to finalize, albeit a bit late and
> perhaps in a broken way.  Still, storage of generator-iterators in module
> globals is a very unlikely scenario, since it's more common to loop over
> such iterators than it is to store them in any kind of variable.

Sure. But I still have some reservations, since cycles can pop up in
the strangest of places (especially when tracebacks are involved --
tracebacks have been causing problems due to cycles and keeping
variables alive almost since Python's inception). I posted about this
a while ago, but don't recall seeing a response that took my fear
away.

Unfortunately, discussing this is about 1000x easier when you have a
shared drawing surface available -- I cannot even think about this
myself without making drawings of object references...

-- 
--Guido van Rossum (home page: http://www.python.org/~guido/)