Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.python > #45099

Re: object.enable() anti-pattern

Path csiph.com!usenet.pasdenom.info!news.etla.org!news.stack.nl!newsfeed.xs4all.nl!newsfeed1.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
Return-Path <oscar.j.benjamin@gmail.com>
X-Original-To python-list@python.org
Delivered-To python-list@mail.python.org
X-Spam-Status OK 0.114
X-Spam-Level *
X-Spam-Evidence '*H*': 0.77; '*S*': 0.00; 'c++,': 0.07; 'agrees': 0.09; 'constructor': 0.09; 'cc:addr:python-list': 0.11; '(and,': 0.16; 'called.': 0.16; 'kern': 0.16; 'roy': 0.16; 'subclass': 0.16; 'thread,': 0.16; 'throw': 0.16; 'wrote:': 0.18; 'separate': 0.22; 'cc:addr:python.org': 0.22; 'earlier': 0.24; 'cc:2**0': 0.24; 'cc:no real name:2**0': 0.24; 'header:In-Reply-To:1': 0.27; 'robert': 0.30; 'then.': 0.30; 'message-id:@mail.gmail.com': 0.30; 'exceptions': 0.31; 'class': 0.32; 'handled': 0.32; 'everyone': 0.33; 'entirely': 0.33; "i'd": 0.34; 'could': 0.34; 'received:209.85': 0.35; 'common': 0.35; 'received:209.85.220': 0.35; 'but': 0.35; 'received:google.com': 0.35; 'there': 0.35; 'c++': 0.36; 'curious': 0.36; 'instances': 0.36; 'method': 0.36; 'should': 0.36; 'virtual': 0.37; 'received:209': 0.37; 'step': 0.37; 'being': 0.38; 'implement': 0.38; 'either': 0.39; 'days': 0.60; 'even': 0.60; 'mentioned': 0.61; 'new': 0.61; 'skip:n 10': 0.64; 'school': 0.64; 'talking': 0.65; 'smith': 0.68; 'article': 0.77; 'doubts': 0.84; 'fail.': 0.84; 'oscar': 0.84; 'subject:skip:o 10': 0.84; 'valid,': 0.84; 'poorly': 0.93; '2013': 0.98
DKIM-Signature v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=x-received:mime-version:in-reply-to:references:from:date:message-id :subject:to:cc:content-type; bh=fgxxPOpxKbY6NuMJ1DFNZ5a0gFSgBMPvBq+31oTJnic=; b=MUaFmxOaIUjGTwnSB/rMZ/mE7QMaJckbwBVA/8uu/xLSnlMWRx9WoQ6N5i52OUphnS zD5Gp6P4ON56u1TKzLw8i6JXlGX6arMpFyzJaqAXuU3BL5eXqNA6FA6zPbqNMG91dOvi 84J+647dE7MgQ3qqi5GvDCwIOH5bltLvvu/lSPIg3No+DFZNHCuGOae3iADt012qxiGV 4PIGQP3Nxi/V+pGNfRz89rL+RDgmTW7Nbt+jswGKhkxx5G6Y+kwa2MjOYnM6JZKzXdpV YLogoNQdKDSA8os5Ady6KxdWQvE2RjbhTT4eUJyUgHhjN67EP4KUjFjHmFpZ3EwxMdQt P9Tg==
X-Received by 10.52.93.78 with SMTP id cs14mr9830601vdb.17.1368196161033; Fri, 10 May 2013 07:29:21 -0700 (PDT)
MIME-Version 1.0
In-Reply-To <roy-F6FC44.10011410052013@news.panix.com>
References <518a123c$0$11094$c3e8da3@news.astraweb.com> <Z1Eit.289$oB7.283@newsfe02.iad> <518b32ef$0$11120$c3e8da3@news.astraweb.com> <roy-8428A6.09074209052013@news.panix.com> <518be931$0$29997$c3e8da3$5496439d@news.astraweb.com> <mailman.1501.1368124461.3114.python-list@python.org> <518c5bbc$0$29997$c3e8da3$5496439d@news.astraweb.com> <roy-6D8B98.23095509052013@news.panix.com> <518c7f8e$0$29997$c3e8da3$5496439d@news.astraweb.com> <Hm0jt.6$I26.5@newsfe26.iad> <518cd360$0$29997$c3e8da3$5496439d@news.astraweb.com> <mailman.1527.1368188358.3114.python-list@python.org> <roy-F6FC44.10011410052013@news.panix.com>
From Oscar Benjamin <oscar.j.benjamin@gmail.com>
Date Fri, 10 May 2013 15:29:00 +0100
Subject Re: object.enable() anti-pattern
To Roy Smith <roy@panix.com>
Content-Type text/plain; charset=ISO-8859-1
Cc python-list@python.org
X-BeenThere python-list@python.org
X-Mailman-Version 2.1.15
Precedence list
List-Id General discussion list for the Python programming language <python-list.python.org>
List-Unsubscribe <http://mail.python.org/mailman/options/python-list>, <mailto:python-list-request@python.org?subject=unsubscribe>
List-Archive <http://mail.python.org/pipermail/python-list/>
List-Post <mailto:python-list@python.org>
List-Help <mailto:python-list-request@python.org?subject=help>
List-Subscribe <http://mail.python.org/mailman/listinfo/python-list>, <mailto:python-list-request@python.org?subject=subscribe>
Newsgroups comp.lang.python
Message-ID <mailman.1530.1368196163.3114.python-list@python.org> (permalink)
Lines 30
NNTP-Posting-Host 2001:888:2000:d::a6
X-Trace 1368196163 news.xs4all.nl 15975 [2001:888:2000:d::a6]:47289
X-Complaints-To abuse@xs4all.nl
Xref csiph.com comp.lang.python:45099

Show key headers only | View raw

On 10 May 2013 15:01, Roy Smith <roy@panix.com> wrote:
> In article <mailman.1527.1368188358.3114.python-list@python.org>,
>  Robert Kern <robert.kern@gmail.com> wrote:
>
>> I'd be curious to see in-the-wild instances of the anti-pattern that
>> you are talking about, then. I think everyone agrees that entirely
>> unmotivated "enable" methods should be avoided, but I have my doubts
>> that they come up very often.
>
> As I mentioned earlier in this thread, this was a common pattern in the
> early days of C++, when exceptions were a new concept and handled poorly
> by many compilers (and, for that matter, programmers).
>
> There was a school of thought that constructors should never be able to
> fail (because the only way for a constructor to fail is to throw an
> exception).  The pattern was to always have the constructor succeed, and
> then either have a way to check to see if the newly-constructed object
> was valid, or have a separate post-construction initialization step
> which could fail.

It's not just because of exceptions. In C++ virtual method calls in a
constructor for a class A will always call the methods of class A even
if the object being constructed is actually of a subclass B because
the B part of the object isn't initialised when the A constructor is
called. There may be a better way to do this since I last used C++ but
as I remember it the two-phase pattern was a recommended way to
implement polymorphic behaviour during initialisation.


Oscar

Back to comp.lang.python | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-08 08:52 +0000
  Re: object.enable() anti-pattern Christian Heimes <christian@python.org> - 2013-05-08 11:51 +0200
  Re: object.enable() anti-pattern Robert Kern <robert.kern@gmail.com> - 2013-05-08 11:13 +0100
    Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-08 12:30 +0000
  Re: object.enable() anti-pattern Roy Smith <roy@panix.com> - 2013-05-08 09:17 -0400
  Re: object.enable() anti-pattern Duncan Booth <duncan.booth@invalid.invalid> - 2013-05-08 14:27 +0000
    Re: object.enable() anti-pattern Dan Sommers <dan@tombstonezero.net> - 2013-05-09 02:38 +0000
      Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-09 05:37 +0000
        Re: object.enable() anti-pattern Chris Angelico <rosuav@gmail.com> - 2013-05-09 15:52 +1000
    Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-09 03:12 +0000
  Re: object.enable() anti-pattern Dan Sommers <dan@tombstonezero.net> - 2013-05-09 02:42 +0000
    Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-09 05:23 +0000
      Re: object.enable() anti-pattern Terry Jan Reedy <tjreedy@udel.edu> - 2013-05-09 02:41 -0400
      Re: object.enable() anti-pattern Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-05-09 19:54 +1200
        Re: object.enable() anti-pattern Cameron Simpson <cs@zip.com.au> - 2013-05-09 18:23 +1000
          Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-09 11:30 +0000
            Re: object.enable() anti-pattern Cameron Simpson <cs@zip.com.au> - 2013-05-10 09:36 +1000
              Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-10 05:00 +0000
                Re: object.enable() anti-pattern Roy Smith <roy@panix.com> - 2013-05-10 01:50 -0400
                Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-10 09:47 +0000
                Re: object.enable() anti-pattern Roy Smith <roy@panix.com> - 2013-05-10 09:22 -0400
                Re: object.enable() anti-pattern Cameron Simpson <cs@zip.com.au> - 2013-05-11 08:25 +1000
                Re: object.enable() anti-pattern Mark Janssen <dreamingforward@gmail.com> - 2013-05-10 20:16 -0700
                Re: object.enable() anti-pattern Thomas Rachel <nutznetz-0c1b6768-bfa9-48d5-a470-7603bd3aa915@spamschutz.glglgl.de> - 2013-05-11 06:21 +0200
                Re: object.enable() anti-pattern Mark Janssen <dreamingforward@gmail.com> - 2013-05-10 21:00 -0700
                Re: object.enable() anti-pattern Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-05-11 15:04 -0400
        Re: object.enable() anti-pattern Greg Ewing <greg.ewing@canterbury.ac.nz> - 2013-05-10 10:56 +1200
      Re: object.enable() anti-pattern Roy Smith <roy@panix.com> - 2013-05-09 09:07 -0400
        Re: object.enable() anti-pattern Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-05-09 14:51 +0100
        Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-09 18:21 +0000
          Re: object.enable() anti-pattern MRAB <python@mrabarnett.plus.com> - 2013-05-09 19:34 +0100
            Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-10 02:30 +0000
              Re: object.enable() anti-pattern Roy Smith <roy@panix.com> - 2013-05-09 23:09 -0400
                Re: object.enable() anti-pattern Mark Janssen <dreamingforward@gmail.com> - 2013-05-09 20:19 -0700
                Re: object.enable() anti-pattern Chris Angelico <rosuav@gmail.com> - 2013-05-10 13:46 +1000
                Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-10 05:03 +0000
                Re: object.enable() anti-pattern Dan Sommers <dan@tombstonezero.net> - 2013-05-10 06:22 +0000
                Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-10 11:00 +0000
                Re: object.enable() anti-pattern Robert Kern <robert.kern@gmail.com> - 2013-05-10 13:19 +0100
                Re: object.enable() anti-pattern Roy Smith <roy@panix.com> - 2013-05-10 10:01 -0400
                Re: object.enable() anti-pattern Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2013-05-10 15:29 +0100
                Re: object.enable() anti-pattern Roy Smith <roy@panix.com> - 2013-05-10 10:37 -0400
                Re: object.enable() anti-pattern Chris Angelico <rosuav@gmail.com> - 2013-05-11 00:46 +1000
                Re: object.enable() anti-pattern Roy Smith <roy@panix.com> - 2013-05-10 10:54 -0400
                Re: object.enable() anti-pattern Chris Angelico <rosuav@gmail.com> - 2013-05-11 01:09 +1000
                Re: object.enable() anti-pattern Roy Smith <roy@panix.com> - 2013-05-10 11:21 -0400
                Re: object.enable() anti-pattern Chris Angelico <rosuav@gmail.com> - 2013-05-11 01:44 +1000
                Re: object.enable() anti-pattern Robert Kern <robert.kern@gmail.com> - 2013-05-10 16:33 +0100
                Re: object.enable() anti-pattern Serhiy Storchaka <storchaka@gmail.com> - 2013-05-10 18:44 +0300
                Re: object.enable() anti-pattern André Malo <ndparker@gmail.com> - 2013-05-11 17:33 +0200
                Re: object.enable() anti-pattern Chris Angelico <rosuav@gmail.com> - 2013-05-12 02:04 +1000
                Re: object.enable() anti-pattern Robert Kern <robert.kern@gmail.com> - 2013-05-10 18:20 +0100
                Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-11 07:51 +0000
                Re: object.enable() anti-pattern Roy Smith <roy@panix.com> - 2013-05-11 09:31 -0400
                Re: object.enable() anti-pattern Robert Kern <robert.kern@gmail.com> - 2013-05-11 20:55 +0100
                Re: object.enable() anti-pattern Chris Angelico <rosuav@gmail.com> - 2013-05-12 08:39 +1000
                Re: object.enable() anti-pattern Chris Angelico <rosuav@gmail.com> - 2013-05-11 03:24 +1000
                Re: object.enable() anti-pattern Mark Janssen <dreamingforward@gmail.com> - 2013-05-10 19:43 -0700
                Re: object.enable() anti-pattern Wayne Werner <wayne@waynewerner.com> - 2013-05-12 11:48 -0500
                Re: object.enable() anti-pattern Terry Jan Reedy <tjreedy@udel.edu> - 2013-05-12 16:23 -0400
                Re: object.enable() anti-pattern Mark Janssen <dreamingforward@gmail.com> - 2013-05-09 20:51 -0700
              Re: object.enable() anti-pattern Chris Angelico <rosuav@gmail.com> - 2013-05-10 13:08 +1000
          Re: object.enable() anti-pattern roy@panix.com (Roy Smith) - 2013-05-09 14:59 -0400
            Re: object.enable() anti-pattern Chris Angelico <rosuav@gmail.com> - 2013-05-10 07:55 +1000
      Re: object.enable() anti-pattern Nobody <nobody@nowhere.com> - 2013-05-10 17:59 +0100
        Re: object.enable() anti-pattern Roy Smith <roy@panix.com> - 2013-05-10 13:32 -0400
          Re: object.enable() anti-pattern Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2013-05-11 15:24 -0400
        Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-11 07:05 +0000
  Re: object.enable() anti-pattern Mark Janssen <dreamingforward@gmail.com> - 2013-05-08 19:53 -0700
  Re: object.enable() anti-pattern Mark Janssen <dreamingforward@gmail.com> - 2013-05-08 19:56 -0700
  Re: object.enable() anti-pattern Wayne Werner <wayne@waynewerner.com> - 2013-05-09 06:08 -0500
    Re: object.enable() anti-pattern Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-05-09 11:51 +0000
    Re: object.enable() anti-pattern Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2013-05-10 11:43 +1200
      Re: object.enable() anti-pattern Michael Speer <knomenet@gmail.com> - 2013-05-09 20:18 -0400
        Re: object.enable() anti-pattern Roy Smith <roy@panix.com> - 2013-05-09 20:50 -0400
      Re: object.enable() anti-pattern Wayne Werner <wayne@waynewerner.com> - 2013-05-12 12:14 -0500
      Re: object.enable() anti-pattern Terry Jan Reedy <tjreedy@udel.edu> - 2013-05-12 16:03 -0400
      Re: object.enable() anti-pattern Greg Ewing <greg.ewing@canterbury.ac.nz> - 2013-05-13 11:18 +1200
      Re: object.enable() anti-pattern Fábio Santos <fabiosantosart@gmail.com> - 2013-05-13 07:32 +0100
      Re: object.enable() anti-pattern Chris Angelico <rosuav@gmail.com> - 2013-05-13 17:36 +1000
      Re: object.enable() anti-pattern Fábio Santos <fabiosantosart@gmail.com> - 2013-05-13 09:09 +0100
      Re: object.enable() anti-pattern Wayne Werner <wayne@waynewerner.com> - 2013-05-13 08:15 -0500

csiph-web