Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!gegeweb.org!de-l.enfer-du-nord.net!feeder1.enfer-du-nord.net!newsfeed.eweka.nl!eweka.nl!feeder3.eweka.nl!newsfeed.xs4all.nl!newsfeed5.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 0.006 X-Spam-Evidence: '*H*': 0.99; '*S*': 0.00; 'called.': 0.09; 'chose': 0.09; 'decorator': 0.09; 'first:': 0.09; 'anyway': 0.09; 'def': 0.13; 'skip:f 30': 0.13; '**kwargs):': 0.16; '*args,': 0.16; 'decorators.': 0.16; 'enlighten': 0.16; 'happens:': 0.16; 'invoked.': 0.16; 'str"': 0.16; 'str):': 0.16; 'cc:addr:python- list': 0.16; 'wrote:': 0.18; 'previously': 0.19; 'cc:no real name:2**0': 0.20; 'trying': 0.21; 'header:In-Reply-To:1': 0.22; 'cc:2**0': 0.24; 'consist': 0.24; 'object,': 0.24; 'skip:_ 20': 0.26; "i'm": 0.26; 'function': 0.27; 'import': 0.27; 'compare': 0.28; 'url:code': 0.28; 'bit': 0.28; 'problem': 0.29; 'cc:addr:python.org': 0.29; 'pm,': 0.29; 'class': 0.29; 'lines': 0.30; 'confused': 0.30; 'object.': 0.30; 'python3': 0.30; 'received:mail-bw0-f46.google.com': 0.30; '(as': 0.31; 'usually': 0.31; 'skip:( 20': 0.31; 'does': 0.32; 'actual': 0.32; 'me?': 0.32; 'received:209.85.214': 0.32; 'implement': 0.32; 'message- id:@gmail.com': 0.33; 'header:User-Agent:1': 0.33; 'actually': 0.33; 'there': 0.33; 'object': 0.33; 'it.': 0.34; 'someone': 0.34; 'checking': 0.34; 'creates': 0.34; 'something': 0.35; 'however,': 0.36; 'starting': 0.36; '(to': 0.37; 'bound': 0.37; 'class.': 0.37; 'two': 0.37; 'but': 0.37; 'reasons': 0.37; 'received:google.com': 0.37; 'skip:_ 10': 0.37; 'could': 0.37; 'received:10.0.0': 0.38; 'received:209.85': 0.38; 'created': 0.38; 'should': 0.39; 'why': 0.39; 'called': 0.40; 'group,': 0.40; 'received:209': 0.40; 'within': 0.60; 'type': 0.61; 'here.': 0.66; 'blank': 0.74; '__call__': 0.84; 'bar:': 0.84; 'checker': 0.93 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=message-id:date:from:user-agent:mime-version:to:cc:subject :references:in-reply-to:content-type:content-transfer-encoding; bh=tZck/6IK9mjD9+cma06SSjf1bA6n+N+n+IKMkbSjf1M=; b=eDjDrl4ZrSjasR82AheLKfhNh+Ub4LiNiY4V1bIEbfKdL6CIa05CwQAwCq4iB1sUEL 3hmWHNdFmGcQyEG5ubYbWmlU4D56KNWMeEm8gehoXq5lVBqWGHcHJdq3/tPoR8Na82ze iOFDqzmcVT6FzLexNACTzTOWTWerOcdSAFr8k= Date: Mon, 12 Dec 2011 13:37:32 +0000 From: Andrea Crotti User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:8.0) Gecko/20111108 Thunderbird/8.0 MIME-Version: 1.0 To: Henrik Faber Subject: Re: Confusion about decorators References: In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Cc: python-list@python.org X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.12 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: 57 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1323697057 news.xs4all.nl 6968 [2001:888:2000:d::a6]:35470 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:17039 On 12/12/2011 01:27 PM, Henrik Faber wrote: > Hi group, > > I'm a bit confused regarding decorators. Recently started playing with > them with Python3 and wanted (as an excercise) to implement a simple > type checker first: I know there are lots of them out there, this is > actually one of the reasons I chose that particular function (to compare > my solution against other, proven solutions). > > Starting with a blank slate, I did something along the lines of: > > class _TypeCheckedFunction(): > def __init__(self, decoratedfunction): > self._decoratedfunction = decoratedfunction > > def __call__(self, *args, **kwargs): > [...] Actual checking > > def typecheck(wrappedfunction): > checkfunction = _TypeCheckedFunction(wrappedfunction) > functools.update_wrapper(checkfunction, wrappedfunction) > return checkfunction > > And decorate my methods like > > @typecheck > def setbar(self, bar: str): > > This works somewhat. The problem is, however, when the method is > actually called. This is what happens: > > 1. The decorator is called upon import of the decorated class. It > creates a _TypeCheckedFunction(setbar) object. > 2. When setbar is actually called (blubb.setbar("fooobar")), the > __call__ method of the previously created _TypeCheckedFunction is invoked. > 3. When trying to call self._decoratedfunction from within that object, > this fails: "self" is missing! self._decoratedfunction is only the > *function*, not the bound function of the object that contains setbar(). > Therefore I cannot proceed here. > > Solutions that I have seen working usually consist of two functions > wrapped in each other, but I do not know why the additional introduction > of a class makes everything fail. > > Can someone please enlighten me? > > Best regards, > Henrik Not sure how that could work in general, what does "bar: str" should do? Is that a dictionary? Anyway there is already an implementation if you're interested for type checking: http://oakwinter.com/code/typecheck/ You can have a look at how they do it.