On 18 September 2017 at 19:48, Antoine Pitrou <solip...@pitrou.net> wrote: > On Mon, 18 Sep 2017 11:31:12 +0200 > Victor Stinner <victor.stin...@gmail.com> wrote: >> >> Ideally, CPython 3.x should never create reference cycles. Removing >> Exception.__traceback__ is the obvious "fix" for the issue. But I >> expect that slowly, a lot of code started to rely on the attribute, >> maybe even for good reasons :-) > > The real issue is not reference cycles, but the fact that a traceback > frame keeps all locals alive. When the frame's execution is finished, > that information is practically almost always useless, but is kept for > the rare cases of debugging (and perhaps dubious features such as > some of py.test's magic).
As another use case, IPython tracebacks will include details of referenced local variables, and https://docs.python.org/3/library/traceback.html#tracebackexception-objects offers the ability to readily capture the repr() of locals referenced from a traceback for the same reason. > So we're constantly paying the price of this > minor, albeit probably useful (*), debugging-related feature with > annoying object lifetime issues that are sometimes quite difficult to > track down and solve. > > (*) (I've hardly ever used pdb so I don't know if people often examine > the locals of finished frames, but I suppose some do) > > Perhaps it would be useful to have a way to tell the interpreter to > automatically clear all locals on frames when they have finished > executing. It could be a thread-local setting (or, better, a PEP 550 > context variable setting). I wonder if it might be reasonable to have tracebacks only hold a weak reference to their frame objects when "__debug__ == False". Cheers, Nick. -- Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia _______________________________________________ Python-Dev mailing list Python-Dev@python.org https://mail.python.org/mailman/listinfo/python-dev Unsubscribe: https://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
