Path: csiph.com!usenet.pasdenom.info!weretis.net!feeder4.news.weretis.net!ecngs!feeder2.ecngs.de!novso.com!newsfeed.xs4all.nl!newsfeed4.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 0.077 X-Spam-Evidence: '*H*': 0.85; '*S*': 0.00; 'subject:Python': 0.06; 'method,': 0.09; 'def': 0.12; 'jan': 0.12; 'fine.': 0.16; 'fly': 0.16; 'y):': 0.16; 'fix': 0.17; 'wrote:': 0.18; 'have:': 0.19; '>>>': 0.22; 'import': 0.22; 'header:User-Agent:1': 0.23; 'fraction': 0.24; 'instead.': 0.24; 'class.': 0.26; 'this:': 0.26; 'header:In-Reply-To:1': 0.27; 'chris': 0.29; 'am,': 0.29; "doesn't": 0.30; 'work.': 0.31; '25,': 0.31; 'gary': 0.31; 'idea,': 0.31; "they'll": 0.31; 'class': 0.32; 'brian': 0.33; 'skip:_ 10': 0.34; 'operations': 0.35; 'but': 0.35; 'add': 0.35; 'false': 0.36; 'method': 0.36; 'should': 0.36; 'skip:- 20': 0.37; 'clear': 0.37; 'to:addr:python-list': 0.38; 'pm,': 0.38; 'that,': 0.38; 'does': 0.39; 'bad': 0.39; 'to:addr:python.org': 0.39; 'how': 0.40; 'ensure': 0.60; 'easy': 0.60; 'most': 0.60; 'new': 0.61; 'more': 0.64; 'charset:windows-1252': 0.65; 'delegate': 0.68; 'institute': 0.72; 'received:204': 0.75; 'dr.': 0.77; '2015': 0.84; 'sorry.': 0.91 Date: Sat, 24 Jan 2015 15:41:17 -0800 From: Gary Herron User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: python-list@python.org Subject: Re: Delegation in Python References: In-Reply-To: Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: 7bit 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: 54 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1422142883 news.xs4all.nl 2837 [2001:888:2000:d::a6]:35203 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:84518 On 01/24/2015 03:22 PM, Chris Angelico wrote: > On Sun, Jan 25, 2015 at 9:57 AM, Brian Gladman wrote: >> But I am not clear on how to delegate from my new class to the existing >> Fraction class. This is what I have: >> >> -------------------------- >> class RF(Fraction): >> >> def __new__(self, x, y): >> super().__new__(self, x, y) >> >> def is_integer(self): >> return self.numerator % self.denominator == 0 >> >> def __getattr__(self, attr): >> return getattr(self, attr) > If you just drop everything but your new method, it should work just fine. > > class RF(Fraction): > def is_integer(self): > return self.numerator % self.denominator == 0 > > However, this doesn't ensure that operations on RFs will return more > RFs - they'll often return Fractions instead. There's no easy fix for > that, sorry. > > ChrisA You can always "monkey-path" the Fraction class on the fly to add a new method to it. I think most would consider this a bad idea, but it does work. Try this: >>> from fractions import Fraction >>> def is_integer(self): ... return self.numerator % self.denominator == 0 ... >>> Fraction.is_integer = is_integer # Monkey-patch Fraction >>> >>> Fraction(1,2).is_integer() False >>> Fraction(2,1).is_integer() True Gary Herron -- Dr. Gary Herron Department of Computer Science DigiPen Institute of Technology (425) 895-4418