[Python-Dev] What is the precise problem? [was: Reference cycles in Exception.__traceback__]

[Mark Shannon]

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.