Path: csiph.com!newsfeed.hal-mli.net!feeder3.hal-mli.net!newsfeed.hal-mli.net!feeder1.hal-mli.net!newsfeed.xs4all.nl!newsfeed3.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 0.000 X-Spam-Evidence: '*H*': 1.00; '*S*': 0.00; 'aggregate': 0.07; 'attribute': 0.07; 'python3': 0.07; 'if,': 0.09; 'line:': 0.09; 'objects,': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'subject:question': 0.10; 'python': 0.11; 'def': 0.12; '"%s"': 0.16; '(1,': 0.16; '(x,': 0.16; '0):': 0.16; 'cleaned': 0.16; 'collections': 0.16; 'possesses': 0.16; 'received:80.91.229.3': 0.16; 'received:dip0.t-ipconnect.de': 0.16; 'received:plane.gmane.org': 0.16; 'received:t-ipconnect.de': 0.16; 'subject:class': 0.16; 'wrote:': 0.18; 'code.': 0.18; 'header :User-Agent:1': 0.23; "i've": 0.25; 'define': 0.26; 'references': 0.26; 'defined': 0.27; 'header:X-Complaints-To:1': 0.27; 'point': 0.28; 'points': 0.29; 'code': 0.31; 'lines': 0.31; 'that.': 0.31; 'container': 0.31; 'class': 0.32; 'lists': 0.32; 'run': 0.32; 'skip:_ 10': 0.34; 'could': 0.34; 'objects': 0.35; 'but': 0.35; 'add': 0.35; 'achieving': 0.36; 'reflect': 0.36; 'subject:regarding': 0.36; 'version:': 0.36; 'starting': 0.37; 'represent': 0.38; 'to:addr:python-list': 0.38; 'does': 0.39; 'to:addr:python.org': 0.39; 'received:org': 0.40; 'space': 0.40; '20,': 0.68; 'ending': 0.78; 'updated,': 0.84; 'trouble.': 0.91 X-Injected-Via-Gmane: http://gmane.org/ To: python-list@python.org From: Peter Otten <__peter__@web.de> Subject: Re: Newbie: question regarding references and class relationships Date: Mon, 10 Jun 2013 15:49:27 +0200 Organization: None References: Mime-Version: 1.0 Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7Bit X-Gmane-NNTP-Posting-Host: p508489f5.dip0.t-ipconnect.de User-Agent: KNode/4.7.3 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: 74 NNTP-Posting-Host: 2001:888:2000:d::a6 X-Trace: 1370872174 news.xs4all.nl 15977 [2001:888:2000:d::a6]:37282 X-Complaints-To: abuse@xs4all.nl Xref: csiph.com comp.lang.python:47557 Rui Maciel wrote: > Let: > - class Point be a data type which is used to define points in space > - class Line be a data type which possesses an aggregate relationship with > objects of type Point > - class Model be a container class which stores collections of Point and > Line objects > > > Essentially, a Model object stores lists of Point objects and Line > objects, and Line objects include references to Point objects which > represent the starting and ending point of a line. > > To reflect this class relationship, I've defined the following classes: > > > class Point: Don't add > position = [] to your code. That's not a declaration, but a class attribute and in the long run it will cause nothing but trouble. > def __init__(self, x, y, z = 0): > self.position = [x, y, z] > > class Line: > points = () > def __init__(self, p_i, p_f): > self.points = (p_i, p_f) > > class Model: > points = [] > lines = [] > > > > > It would be nice if, whenever a Point object was updated, the Line objects > which are associated with it could reflect those updates directly in > Line.p_i and Line.p_f. > > What's the Python way of achieving the same effect? Your code already does that. Here's a minimally cleaned up version: $ cat tmp_points.py class Point: def __init__(self, x, y, z=0): self.position = (x, y, z) def __str__(self): return "%s" % (self.position,) class Line: def __init__(self, p_i, p_f): self.points = (p_i, p_f) def __str__(self): return "%s-->%s" % self.points a = Point(1, 2, 3) b = Point(4, 5, 6) ab = Line(a, b) print(ab) a.position = (10, 20, 30) print(ab) $ python3 tmp_points.py (1, 2, 3)-->(4, 5, 6) (10, 20, 30)-->(4, 5, 6)