Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.002 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'that?': 0.05; 'pypy': 0.07; 'received:openend.se': 0.09; 'received:theraft.openend.se': 0.09; 'reports.': 0.09; 'subject:skip:m 10': 0.09; 'cc:addr :python-list': 0.10; 'python': 0.11; '2.7': 0.13; 'cc:addr:lac': 0.16; 'cc:addr:openend.se': 0.16; 'from:addr:lac': 0.16; 'from:addr:openend.se': 0.16; 'from:name:laura creighton': 0.16; 'reproduce': 0.16; 'to:addr:pearwood.info': 0.16; "to:name:steven d'aprano": 0.16; 'laura': 0.18; 'runs': 0.18; 'cc:addr:python.org': 0.21; 'cc:2**1': 0.22; 'do.': 0.22; '"",': 0.22; 'gcc': 0.22; 'title,': 0.22; '2015': 0.23; 'header:In-Reply- To:1': 0.24; '(most': 0.24; 'url:bugs': 0.24; 'prints': 0.29; 'received:se': 0.29; 'cc:no real name:2**1': 0.29; 'fri,': 0.31; 'error.': 0.31; "can't": 0.32; 'anyone': 0.32; 'probably': 0.32; 'url:python': 0.33; 'traceback': 0.33; '(for': 0.34; 'file': 0.34; 'reply.': 0.35; 'but': 0.36; 'url:org': 0.36; 'there': 0.36; 'so,': 0.37; 'should': 0.37; 'operating': 0.37; 'subject:: ': 0.37; 'charset:us-ascii': 0.37; 'version': 0.38; 'system.': 0.39; 'your': 0.60; 'necessarily': 0.61; 'header:Message-Id:1': 0.62; 'more': 0.62; 'mar': 0.65; 'reply': 0.67; 'jul': 0.72; '.....': 0.76; '+1000,': 0.84 To: "Steven D'Aprano" cc: python-list@python.org, lac@openend.se From: Laura Creighton Subject: Re: Bug in floating point multiplication In-Reply-To: Message from "Steven D'Aprano" of "Fri, 03 Jul 2015 00:52:55 +1000." <55955048$0$1662$c3e8da3$5496439d@news.astraweb.com> References: <55955048$0$1662$c3e8da3$5496439d@news.astraweb.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-ID: <31536.1436050443.1@theraft> Date: Sun, 05 Jul 2015 00:54:03 +0200 X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.3.9 (theraft.openend.se [127.0.0.1]); Sun, 05 Jul 2015 00:54:06 +0200 (CEST) X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.20+ 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: 49 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1436050467 news.xs4all.nl 2889 [2001:888:2000:d::a6]:45185 X-Complaints-To: abuse@xs4all.nl Path: csiph.com!usenet.pasdenom.info!news.stben.net!border1.nntp.ams1.giganews.com!nntp.giganews.com!newsfeed.xs4all.nl!newsfeed8.news.xs4all.nl!newsgate.cistron.nl!newsgate.news.xs4all.nl!post.news.xs4all.nl!not-for-mail Xref: csiph.com comp.lang.python:93495 In a message of Fri, 03 Jul 2015 00:52:55 +1000, "Steven D'Aprano" writes: >Despite the title, this is not one of the usual "Why can't Python do >maths?" "bug" reports. > >Can anyone reproduce this behaviour? If so, please reply with the version of >Python and your operating system. Printing sys.version will probably do. > > >x = 1 - 1/2**53 >assert x == 0.9999999999999999 >for i in range(1, 1000000): > if int(i*x) == i: > print(i); break > > >Using Jython and IronPython, the loop runs to completion. That is the >correct behaviour, or so I am lead to believe. Using Python 2.6, 2.7 and >3.3 on Centos and Debian, it prints 2049 and breaks. That should not >happen. If you can reproduce that (for any value of i, not necessarily >2049), please reply. > >See also http://bugs.python.org/issue24546 for more details. > > > >-- >Steven PyPy says: Python 2.7.9 (2.5.1+dfsg-1, Mar 27 2015, 19:45:43) [PyPy 2.5.1 with GCC 4.9.2] on linux2 Type "help", "copyright", "credits" or "license" for more information. >>>> x = 1 - 1/2**53 >>>> assert x == 0.9999999999999999 Traceback (most recent call last): File "", line 1, in AssertionError >>>> for i in range(1, 1000000): .... if int(i*x) == i: .... print(i); break .... .... 1 >>>> So the loop terminates, but there is an Assertion Error. Did you want that? Laura