On Sat, 15 Jun 2013 14:57:49 +1000 Nick Coghlan <ncogh...@gmail.com> wrote:
> On 15 June 2013 03:34, Antoine Pitrou <solip...@pitrou.net> wrote: > > On Wed, 5 Jun 2013 09:10:54 -0700 > > Benjamin Peterson <benja...@python.org> wrote: > >> I (and Guido) are accepting PEP 442 (Safe object finalization) on the > >> condition that finalizers are only ever called once globally. > > > > Ok, so there's an issue with that condition: it can't be upholded on > > non-GC objects. Creating a non-GC object is quite obscure and rare, > > though, since it requires basically a class with no __dict__ and an > > empty __slots__: > > > > class C: > > __slots__ = () > > survivors = [] > > > > def __del__(self): > > self.survivors.append(self) > > > > > > In this case, a C instance's __del__ will be called every time > > destruction is attempted, not only once. Is that a realistic problem? > > So, to trigger that __del__() method a second time, such an object > would have to be: > > 1. Defined in the first place (the use cases for stateless objects > with destructors seem rare...) > 2. Hanging off a reference cycle > 3. Which then gets resurrected They don't need to hang off a reference cycle. You can resurrect a non-cyclic object from __del__ too. But, yeah, stateless objects must be pretty rare, since by definition they cannot represent anything (except perhaps "nothing"). > i.e. force them to be GC-aware when they > define a __del__ method, since they may still be hanging off the edge > of a reference cycle, even if they can't form one themselves Objects which hang off the edge of a reference cycle don't need to be GC-aware, since traversing them isn't needed to be break the cycle. I think "chalking it up as a CPython wart" is a reasonable solution, I just wanted to ask. Regards Antoine. _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
