[Python-Dev] What is the precise problem? [was: Reference cycles in Exception.traceback] (original) (raw)

Mark Shannon mark at hotpy.org
Mon Mar 10 10:45:44 CET 2014

On 08/03/14 15:30, Maciej Fijalkowski wrote:

On Sat, Mar 8, 2014 at 5:14 PM, Victor Stinner <victor.stinner at gmail.com> wrote:

2014-03-08 14:33 GMT+01:00 Antoine Pitrou <solipsis at pitrou.net>:

Ok, it's actually quite trivial. The whole chain is kept alive by the "fut" global variable. If you arrange for it to be disposed of:

fut = asyncio.Future() asyncio.Task(func(fut)) del fut [etc.] then the problem disappears: as soon as gc.collect() happens, the MyObject instance is destroyed, the future is collected, and the future's traceback is printed out. Well, the problem is more general than this specific example. I would like to implement a general solution which would not hold references to local variables, to destroy objects when Python exits the except block. It looks like a "exception summary" containing only data to format the traceback would fit asyncio needs. If you don't want it in the traceback module, I will try to implement it in asyncio. It would be nice to provide an "exception summary" in the traceback module, because it looks like reference cycles related to exception and/or traceback is a common issue (see the list of links I gave in a previous email). Victor How about fixing cyclic gc to deal with del instead? That sounds like an awful change to the semantics.

+1

Cheers, Mark.

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