Path: csiph.com!fu-berlin.de!uni-berlin.de!not-for-mail From: Robin Becker Newsgroups: comp.lang.python Subject: str(float) python 3 versus 2.7 Date: Mon, 23 May 2016 17:39:28 +0100 Lines: 32 Message-ID: References: <7c1af35c-1ac7-96c7-3cba-ab9c8e542d8e@chamonix.reportlab.co.uk> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Trace: news.uni-berlin.de gSHYslldf3MDtTq1CDATegDuR0O9X3EFna/YoAwtpR2A== Return-Path: X-Original-To: python-list@python.org Delivered-To: python-list@mail.python.org X-Spam-Status: OK 0.001 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'nicely': 0.07; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'rounding': 0.09; 'subject:2.7': 0.09; 'python': 0.10; '2.7': 0.13; 'subject:python': 0.14; '0.6': 0.16; 'labels,': 0.16; 'naive': 0.16; 'received:80.91.229.3': 0.16; 'received:io': 0.16; 'received:plane.gmane.org': 0.16; 'received:psf.io': 0.16; 'subject:versus': 0.16; 'string': 0.17; 'figures': 0.18; 'numerical': 0.18; 'all,': 0.20; 'prevent': 0.20; 'object.': 0.22; 'suppose': 0.22; 'leave': 0.23; 'errors': 0.23; 'header:User- Agent:1': 0.26; 'header:X-Complaints-To:1': 0.26; 'function': 0.28; 'behaviour': 0.29; 'issues.': 0.29; 'sensible': 0.29; 'str': 0.29; 'starts': 0.29; 'compared': 0.30; 'up.': 0.32; 'computing': 0.32; 'subject:) ': 0.32; 'class': 0.33; 'skip:c 30': 0.35; 'but': 0.36; 'should': 0.36; 'there': 0.36; 'to:addr:python-list': 0.36; 'being': 0.37; 'received:org': 0.37; 'difference': 0.38; 'skip:- 20': 0.39; 'format': 0.39; 'to:addr:python.org': 0.40; 'some': 0.40; 'suitable': 0.61; 'show': 0.62; 'received:109': 0.75; '2.7.': 0.84; '3.4': 0.84; 'becker': 0.84 X-Injected-Via-Gmane: http://gmane.org/ X-Gmane-NNTP-Posting-Host: 109.174.168.73 X-Mozilla-News-Host: news://news.gmane.org:119 User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.1.0 X-BeenThere: python-list@python.org X-Mailman-Version: 2.1.22 Precedence: list List-Id: General discussion list for the Python programming language List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-Mailman-Original-Message-ID: <7c1af35c-1ac7-96c7-3cba-ab9c8e542d8e@chamonix.reportlab.co.uk> Xref: csiph.com comp.lang.python:109006 I had always imagined that the str founction did some kind of rounding on floats to prevent small numerical errors from showing up. The 2.7 documentation starts like this > class str(object='') > Return a string containing a nicely printable representation of an object. For s However, I see a difference in the behaviour of python3.3, 3.4 & 3.5 when compared to python 2.7. > C:\Users\rptlab>\python33\python.exe -c"print(str(3*0.2))" > 0.6000000000000001 > > C:\Users\rptlab>\python34\python.exe -c"print(str(3*0.2))" > 0.6000000000000001 > > C:\Users\rptlab>\python35\python.exe -c"print(str(3*0.2))" > 0.6000000000000001 > > C:\Users\rptlab>\python27\python.exe -c"print(str(3*0.2))" > 0.6 I suppose I am being naive and should use the round function when computing tick labels, but that leads to other issues. Is there a sensible way to take a set of floats and find a suitable format to show significant figures for all, but leave off the noise? -- Robin Becker