Konrad Schwarz <konrad.schw...@gmail.com> added the comment:
> If I understand correctly, the reported bug is that you're seeing a weakref > callback being executed > after the weakref.ref instance it's attached to is deleted. Is that correct? Exactly. I del what should be the only reference to the weakref.ref/proxy, then del the weakref.ref's referent. The weakref.ref's callback is executed. > Do you have a minimal example we can use to reproduce the effect? Without > such an example, there's not > much of a realistic path to moving this forward. Unfortunately, not at the moment. > However, my suspicion is that that's not what's actually happening here. I > suspect that when you say > "after the corresponding weak reference has been deleted with del", that the > "del" statement you refer > to is not actually deleting the last reference to the weakref.ref object, so > the weakref still exists > after the "del". One easy way that this could happen is if the weakref is > part of a reference cycle > (and I know from personal experience that it's horribly easy to accidentally > *create* reference cycles > via weakref callbacks, especially if those callbacks refer to instance > methods). I tried to be as punctilious as I could to prevent this sort of thing from happening. The weird thing is that the error does not occur when I single step the code in PDB. It must be something internal to CPython, some sort of optimization. Are local variables/stack frames cleaned lazily? Is the last accessed value of a dictionary cached internally, increasing its reference count? I've worked around the problem by double checking in the callback method that it actually should execute; i.e. in my case, that the object has not been removed (del) from a dictionary (which should be the single reference to the object). If the problem does indeed lie with CPython, but has too much of a performance/maintenance impact, perhaps a caveat could be added to the documentation to the effect of "The lifetime of an object may be longer than what a programmer expects causing a weakref's callback to be invoked at a surprising time; it is good practice to program the callback defensively." ---------- _______________________________________ Python tracker <rep...@bugs.python.org> <https://bugs.python.org/issue43383> _______________________________________ _______________________________________________ Python-bugs-list mailing list Unsubscribe: https://mail.python.org/mailman/options/python-bugs-list/archive%40mail-archive.com
