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[Python-Dev] Evil reference cycles caused Exception.__traceback__

Antoine Pitrou solipsis at pitrou.net
Mon Sep 18 06:52:17 EDT 2017 
On Mon, 18 Sep 2017 20:35:02 +1000
Nick Coghlan <ncoghlan at gmail.com> wrote:
> On 18 September 2017 at 20:18, Victor Stinner <victor.stinner at gmail.com> wrote:
> > 2017-09-18 12:07 GMT+02:00 Nick Coghlan <ncoghlan at gmail.com>:  
> >> I wonder if it might be reasonable to have tracebacks only hold a weak
> >> reference to their frame objects when "__debug__ == False".  
> >
> > Please don't change the Python behaviour depending on __debug__, or it
> > will be a nightmare to debug it :-( ("Why does it work on my
> > computer?")  
> 
> Yeah, that's always a challenge :)
> 
> Rather than being thread local or context local state, whether or not
> to keep the full frames in the traceback could be a yet another
> setting on the *exception* object, whereby we tweaked the logic that
> drops the reference at the end of an except clause as follows:

That doesn't solve the problem, since the issue is that exceptions can
be raised (and then silenced) in many places, and you don't want such
exception-raising code (such as socket.create_connection) to start
having to set an option on the exceptions it raises.

Regards

Antoine.
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