Path: csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!weretis.net!feeder1.news.weretis.net!feeder.erje.net!newsfeed.xs4all.nl!newsfeed6.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 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'cpython': 0.05; 'instance,': 0.05; 'pointer': 0.05; 'warnings': 0.05; 'initialize': 0.07; 'exceptions': 0.09; 'match.': 0.09; 'proximity': 0.09; 'tuple': 0.09; 'api': 0.09; 'am,': 0.12; 'cc:addr:python-list': 0.15; '(aka': 0.16; 'subject:syntax': 0.16; 'subject:question': 0.16; 'wrote:': 0.16; 'meant': 0.17; 'wed,': 0.17; 'written': 0.19; 'jan': 0.19; 'cheers,': 0.20; 'cc:no real name:2**0': 0.21; "doesn't": 0.22; 'feb': 0.22; 'header:In-Reply- To:1': 0.22; 'url:dev': 0.23; 'cc:2**0': 0.25; 'code': 0.25; 'saying': 0.25; 'pm,': 0.26; 'function': 0.27; 'code,': 0.27; 'raise': 0.28; 'message-id:@mail.gmail.com': 0.28; 'cc:addr:python.org': 0.29; 'booth': 0.30; 'tuples': 0.30; 'chris': 0.30; 'does': 0.32; 'tue,': 0.32; 'received:209.85.212': 0.34; 'anything': 0.34; "we're": 0.34; 'nested': 0.34; 'null': 0.34; 'url:python': 0.36; 'similar': 0.36; 'reference': 0.37; 'but': 0.37; 'received:google.com': 0.37; 'skip:_ 10': 0.37; 'received:209.85': 0.38; 'think': 0.38; 'url:docs': 0.39; 'url:org': 0.39; 'why': 0.39; 'received:209': 0.39; 'subject:: ': 0.39; 'carry': 0.62; '31,': 0.64; 'absolutely': 0.98 DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=mime-version:in-reply-to:references:from:date:message-id:subject:to :cc:content-type; bh=Vju24TqgqzxHHR6s+TC8wQ9VG9XIi2v/mNUv8urripg=; b=UflOTFwn6KHblxTQYD6HmOdns78ontdiEiiGAL/AHdV7jFMvnKL6jeVTU+rOY8anoc POzUvxGzRDDcYfQPjmbPV+viqWprCBO0KFODlN/5dshEeBb9036a/j0HMvWq8BYlm5g4 GIV8Im2yCdqn9RSwQ4vXfohkA76vYx8vzDfCQ= MIME-Version: 1.0 In-Reply-To: References: From: Ian Kelly Date: Tue, 31 Jan 2012 18:09:21 -0700 Subject: Re: except clause syntax question To: Chris Angelico Content-Type: text/plain; charset=ISO-8859-1 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: 24 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1328058593 news.xs4all.nl 6881 [2001:888:2000:d::a6]:49053 X-Complaints-To: abuse@xs4all.nl Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:19673 On Tue, Jan 31, 2012 at 5:53 PM, Chris Angelico wrote: > On Wed, Feb 1, 2012 at 9:03 AM, Duncan Booth > wrote: >> Abitrarily nested tuples of exceptions cannot contain loops so the code >> simply needs to walk through the tuples until it finds a match. > > Is this absolutely guaranteed? The C API for CPython provides: > (Py2) http://docs.python.org/c-api/tuple.html#PyTuple_SetItem > (Py3) http://docs.python.org/dev/c-api/tuple.html#PyTuple_SetItem > > which doesn't have massive warnings on it saying "USE THIS ONLY TO > INITIALIZE A TUPLE" (compare, for instance, _PyTuple_Resize which does > carry a similar warning). Is the assumption then that we're all > adults, and that mutating a tuple is like passing a null pointer to an > API function (aka "loaded gun in proximity to foot")? I don't know why the docs are written the way that they are, but if you check the code, you can see that PyTuple_SetItem will raise a SystemError if the reference count is anything other than 1. So I think that it is only meant to be used with similar caution and restraint. Cheers, Ian