[Python-Dev] anonymous blocks (don't combine them with generator finalization)

Brett C. bac at OCF.Berkeley.EDU
Fri Apr 22 06:28:42 CEST 2005

Bob Ippolito wrote:
> On Apr 21, 2005, at 8:59 PM, Josiah Carlson wrote:
>> Guido van Rossum <gvanrossum at gmail.com> wrote:
>>> [Brett]
>>>> I think I agree with Samuele that it would be more pertinent to put
>>>> all of this
>>>> effort into trying to come up with some way to handle cleanup in a
>>>> generator.
>>> I.e. PEP 325.
>>> But (as I explained, and you agree) that still doesn't render PEP 310
>>> unnecessary, because abusing the for-loop for implied cleanup
>>> semantics is ugly and expensive, and would change generator semantics;
>>> and it bugs me that the finally clause's reachability depends on the
>>> destructor executing.
>> Yes and no.  PEP 325 offers a method to generators that handles cleanup
>> if necessary and calls it close().  Obviously calling it close is a
>> mistake.  Actually, calling it anything is a mistake, and trying to
>> combine try/finally handling in generators with __exit__/close (inside
>> or outside of generators) is also a mistake.
>> Start by saying, "If a non-finalized generator is garbage collected, it
>> will be finalized."  Whether this be by an exception or forcing a return,
>> so be it.
>> If this were to happen, we have generator finalization handled by the
>> garbage collector, and don't need to translate /any/ for loop.  As long
>> as the garbage collection requirement is documented, we are covered
>> (yay!).
> Well, for the CPython implementation, couldn't you get away with using
> garbage collection to do everything?  Maybe I'm missing something..


Well, if you are missing something then so am I since your suggestion is
basically correct.  The only issue is that people will want more immediate
execution of the cleanup code which gc cannot guarantee.  That's why the
ability to call a method with the PEP 325 approach gets rid of that worry.


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