[Python-Dev] Re: Pre-existing bug of the millennium (so far)

[Tim Peters]

[Tim]
> ...
>> Anyone have a bright idea?  It's remarkable how long we've managed to go
>> without noticing that everything is disastrously broken here <0.9 wink>.

[Jim]
> Sure.  Clearing cyclic trash can call Python code.  If there
> are weakrefs to any of the cyclic trash, then those wekrefs can
> be used to resurrect the objects.  Therefore, *before* clearing cyclic
> trash, we need to remove any weakrefs.  If any of the weakrefs
> being removed have callbacks, then we need to save the callbacks
> and call them *after* all of the weakrefs have been cleared.

Thanks!  Neil Schemenauer and I got together today, and talked each
other into believing this can be made to work, and that it's likely
the best solution too.

The devil's in the details, but this a generalization of the last
round of weakref vs. gc bugfixes, which got the effect of what you
suggest here except only for cyclic-trash weakref objects with weakref
callbacks.  It needs generalization to all weakly-referenced
cyclic-trash objects.  Still unsure how hard that will be to code up,
but am sure it will fix all the test cases I concocted.