On Mon, 18 Sep 2017 20:07:42 +1000 Nick Coghlan <ncoghlan@gmail.com> wrote:
On 18 September 2017 at 19:48, Antoine Pitrou <solipsis@pitrou.net> wrote:
On Mon, 18 Sep 2017 11:31:12 +0200 Victor Stinner <victor.stinner@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.
True... but interactive use has different concerns than production use (hence my proposition of a setting to change frame cleanup behaviour). Besides, IPython also stores the history of displayed values, which is another cause of keeping objects alive :-) Regards Antoine.