> -----Original Message----- > From: python-dev-bounces+kristjan=ccpgames....@python.org > [mailto:python-dev-bounces+kristjan=ccpgames....@python.org] On Behalf > Of Antoine Pitrou > Sent: 8. desember 2009 14:55 > To: python-dev@python.org > Subject: Re: [Python-Dev] recursive closures - reference cycle > > Kristján Valur Jónsson <kristjan <at> ccpgames.com> writes: > > > > The problem with this is that once you have called > > factorial() once, you end up with a recursive cycle. > > You don't need a closure to exhibit a reference cycle. A global > function is > enough: > > >>> def helper(n): > ... if n: > ... return n*helper(n-1) > ... else: > ... return 1 > ... > >>> helper.func_globals['helper'] is helper > True > yes, because: func_globals is globals() == True
You don't need recursion for this to be true. And as soon as you delete "helper" from globals() it goes away. w = wearref.weakref(helper) del helper w() == False. > > If you really want to avoid this you can prevent the function from > depending > on its outside environment: > > >>> from functools import partial > >>> def helper2(rec, n): > ... if n: > ... return n*rec(rec, n-1) > ... else: > ... return 1 > ... > >>> factorial = partial(helper2, helper2) > >>> "helper2" in factorial.func.func_globals > True > >>> del helper2 > >>> "helper2" in factorial.func.func_globals > False > >>> factorial(3) > 6 Interesting, pass itself in as an argument. Yes, there are ways around this, I know. But you have to agree that it is unexpected, no? Somethign for the "reference cycle FAQ." Anyway, I´ll return to my lair now, thanks for your time python-dev :) K _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
