Path: csiph.com!usenet.pasdenom.info!gegeweb.org!de-l.enfer-du-nord.net!feeder1.enfer-du-nord.net!feeds.phibee-telecom.net!newsfeed.xs4all.nl!newsfeed2.news.xs4all.nl!xs4all!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 0.137 X-Spam-Level: * X-Spam-Evidence: '*H*': 0.73; '*S*': 0.01; '(except': 0.07; 'binary': 0.07; 'imply': 0.09; '12:50': 0.16; 'implies': 0.16; 'rounding': 0.16; 'saying.': 0.16; 'special.': 0.16; 'wrote:': 0.18; 'wed,': 0.18; 'header:User-Agent:1': 0.23; 'error': 0.23; '(or': 0.24; 'compare': 0.26; 'header:In-Reply-To:1': 0.27; 'point': 0.28; 'am,': 0.29; "doesn't": 0.30; 'statement': 0.30; 'usually': 0.31; 'decimal': 0.31; 'steven': 0.31; 'another': 0.32; 'could': 0.34; 'equal': 0.35; 'but': 0.35; 'thanks': 0.36; 'error.': 0.37; 'two': 0.37; 'being': 0.38; 'represent': 0.38; 'to:addr:python-list': 0.38; 'pm,': 0.38; 'itself': 0.39; 'to:addr:python.org': 0.39; 'even': 0.60; 'ian': 0.60; 'problems.': 0.60; 'numbers': 0.61; "you're": 0.61; 'more': 0.64; 'different': 0.65; 'received:74.208': 0.68; 'obvious': 0.74; 'special': 0.74; '5.4': 0.84; 'calculations': 0.84; 'received:74.208.4.194': 0.84; 'rusi': 0.91; '2013': 0.98 Date: Wed, 29 May 2013 20:23:00 -0400 From: Dave Angel User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130510 Thunderbird/17.0.6 MIME-Version: 1.0 To: python-list@python.org Subject: Re: Short-circuit Logic References: <5f101d70-e51f-4531-9153-c92ee2486fd9@googlegroups.com> <51a1fc7b$0$30002$c3e8da3$5496439d@news.astraweb.com> <2abf4e9c-8c3b-4e2f-80c9-50c1f1d75c9d@googlegroups.com> <51a4b5a1$0$29966$c3e8da3$5496439d@news.astraweb.com> <04b90c02-833a-4bad-88ad-ab71178b8f79@googlegroups.com> <48519aa0-d0cd-4ffc-a2f5-2107465321d8@qn4g2000pbc.googlegroups.com> In-Reply-To: Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Provags-ID: V02:K0:rgT0yHdfeWPNXJdEtDv9RjgkGf00dUvGLURVbUcHlgc mfh2DHQMclgFGqIRWx99Fb/1FH1vwat196LMrU9VYFFbPObL6X TpKgZkXWPPYuu9MRYD4hSeU3OW8A0/K8PMuc84Yu4C5tNm5wvN es42TuP6qEck8ptCgjgMRL8iaA3Eaf/nOaLlclqZlZGQRdFMBm 9TQQZS2+XGXujPZNm2MB9XalKFOHiSV9kCmwTGn14eShcz5QPB gBz/cLOJHDBtLiyatPLCY0H5h+mtWxUh1vbKnHk05eSmtt5bTU BDvKAVcnudt22FAa0L2WXv4ZsXhK4TSrHYMw7PaLGEMdKMXJvt Onuug5WKPaiPjBltU/Cg= 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: 28 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1369873394 news.xs4all.nl 15918 [2001:888:2000:d::a6]:59853 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:46420 On 05/29/2013 12:50 PM, Ian Kelly wrote: > On Wed, May 29, 2013 at 8:33 AM, rusi wrote: >> 0.0 == 0.0 implies 5.4 == 5.4 >> is not a true statement is what (I think) Steven is saying. >> 0 (or if you prefer 0.0) is special and is treated specially. > > It has nothing to do with 0 being special. A floating point number > will always equal itself (except for nan, which is even more special), > and in particular 5.4 == 5.4. But if you have two different > calculations that produce 0, or two different calculations that > produce 5.4, you might actually get two different numbers that > approximate 0 or 5.4 thanks to rounding error. If you then compare > those two ever-so-slightly different numbers, you will find them > unequal. > Rounding error is just one of the problems. Usually less obvious is quantization error. If you represent a floating number in decimal, but you're using a binary floating point representation, it just might change. Another error is roundoff error. Even in a pure decimal system of (say) 40 digits, I could type in a 42 digit number and it would get quantized. So just because two 42 digit numbers are different doesn't imply that the 40 digit internal format would be. -- DaveA