Path: csiph.com!usenet.pasdenom.info!gegeweb.org!usenet-fr.net!nerim.net!novso.com!newsfeed.xs4all.nl!newsfeed3.news.xs4all.nl!xs4all!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.073 X-Spam-Evidence: '*H*': 0.85; '*S*': 0.00; 'nasty': 0.07; 'bits': 0.09; 'callback': 0.09; 'naturally': 0.09; 'objects,': 0.09; 'python': 0.11; 'creates': 0.14; 'design?': 0.16; 'weird': 0.16; 'thanks,': 0.17; 'code.': 0.18; 'all,': 0.19; 'not,': 0.20; 'earlier': 0.24; 'question': 0.24; 'first,': 0.26; 'certain': 0.27; 'developing': 0.27; 'idea': 0.28; "i'm": 0.30; 'code': 0.31; 'that.': 0.31; 'accidentally': 0.31; 'themselves': 0.32; 'url:python': 0.33; 'everyone': 0.33; 'could': 0.34; 'problem': 0.35; 'objects': 0.35; 'received:google.com': 0.35; 'there': 0.35; 'version': 0.36; 'really': 0.36; 'charset:us-ascii': 0.36; 'url:org': 0.36; 'should': 0.36; 'project': 0.37; 'message- id:@gmail.com': 0.38; 'url:library': 0.38; 'to:addr:python-list': 0.38; 'bad': 0.39; 'sure': 0.39; 'to:addr:python.org': 0.39; 'users': 0.40; 'skip:u 10': 0.60; 'worry': 0.60; 'url:3': 0.61; 'header:Message-Id:1': 0.63; 'kept': 0.65; 'subject:Design': 0.78; 'inform': 0.78; '3.4': 0.84; 'about?': 0.84; 'preventing': 0.84; 'situations,': 0.84; 'subject:thought': 0.84; 'bounce': 0.91 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=from:content-type:content-transfer-encoding:subject:message-id:date :to:mime-version; bh=dZ0ufj9ynbtfJx5uIoDygbvs2uiKvdx+/8ONU5cAdro=; b=jsQLGkAt+V01t7Xj7iPckdLW9b1T5ZiAjgMEjQIbdEGeEv7YksH0hRHMIGxkR4K5XU R3RCe5qU9+KKsRQ19WpwR9i/IW7SnQywUk0eHnsCq9MMqKSQZIqFK6Qq7wPbPTESfJSA FO+r8WLubwECKG9NFNYx4vtW+BV9ZAHpSdSVRxHHmRnYzH/h8jSVtpQ/bCYXwghy9xZQ X8uxUfbsAXqevm3A2ShhAdpErtgWzrNQY5fGlcwOIRCVJ1Fp0Epd0WKKm+/PPXco0Vdl Vpraq7Wb8Tg1cbEwwVpIYKkEnt1k2q0qjAlAwQLaJP+DcmAXD4s1yzM5eyCkZm5791Sm KqPw== X-Received: by 10.140.150.146 with SMTP id 140mr1737836qhw.66.1424486667482; Fri, 20 Feb 2015 18:44:27 -0800 (PST) From: Cem Karan Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: quoted-printable Subject: Design thought for callbacks Date: Fri, 20 Feb 2015 21:44:25 -0500 To: "comp.lang.python" Mime-Version: 1.0 (Mac OS X Mail 6.6 \(1510\)) X-Mailer: Apple Mail (2.1510) X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.15 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Newsgroups: comp.lang.python Message-ID: Lines: 21 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1424486670 news.xs4all.nl 2918 [2001:888:2000:d::a6]:40162 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:86007 Hi all, I'm working on a project that will involve the use of callbacks, = and I want to bounce an idea I had off of everyone to make sure I'm not = developing a bad idea. Note that this is for python 3.4 code; I don't = need to worry about any version of python earlier than that. In order to inform users that certain bits of state have changed, I = require them to register a callback with my code. The problem is that = when I store these callbacks, it naturally creates a strong reference to = the objects, which means that if they are deleted without unregistering = themselves first, my code will keep the callbacks alive. Since this = could lead to really weird and nasty situations, I would like to store = all the callbacks in a WeakSet = (https://docs.python.org/3/library/weakref.html#weakref.WeakSet). That = way, my code isn't the reason why the objects are kept alive, and if = they are no longer alive, they are automatically removed from the = WeakSet, preventing me from accidentally calling them when they are = dead. My question is simple; is this a good design? If not, why not? = Are there any potential 'gotchas' I should be worried about? Thanks, Cem Karan=