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

Groups > comp.lang.python > #40819

Re: Interesting list() un-optimization

Path csiph.com!newsfeed.hal-mli.net!feeder3.hal-mli.net!newsfeed.hal-mli.net!feeder2.hal-mli.net!de-l.enfer-du-nord.net!feeder2.enfer-du-nord.net!cs.uu.nl!news.stack.nl!newsfeed.xs4all.nl!newsfeed4.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
Return-Path <ian.g.kelly@gmail.com>
X-Original-To python-list@python.org
Delivered-To python-list@mail.python.org
X-Spam-Status OK 0.106
X-Spam-Level *
X-Spam-Evidence '*H*': 0.79; '*S*': 0.00; 'cursor': 0.09; 'underlying': 0.09; 'subject:optimization': 0.16; 'wrote:': 0.17; 'stefan': 0.17; 'thu,': 0.17; 'all,': 0.21; 'thanks.': 0.21; 'header:In-Reply-To:1': 0.25; 'message-id:@mail.gmail.com': 0.27; 'subject:list': 0.28; 'efficiently': 0.29; 'large.': 0.29; 'skip:_ 10': 0.29; 'that.': 0.30; 'query': 0.30; 'implement': 0.32; 'could': 0.32; 'to:addr:python-list': 0.33; 'that,': 0.34; "can't": 0.34; 'received:google.com': 0.34; 'returning': 0.35; 'doing': 0.35; 'pm,': 0.35; 'really': 0.36; "didn't": 0.36; 'anything': 0.36; 'does': 0.37; 'rather': 0.37; 'subject:: ': 0.38; 'object': 0.38; 'to:addr:python.org': 0.39; 'subject:-': 0.40; 'back': 0.62; 'skip:n 10': 0.63; 'limit': 0.65; 'manner': 0.74; '2013': 0.84; 'presumably': 0.84; 'to:name:python': 0.84
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:content-type; bh=0Jcosl/VYGTzahmbqvNNzmKAU2Spl4hau4crW6pLkjo=; b=bxpfQaYIWSx7G56DzyvFDFlQDO/8Ajt8hqRgmkXhG6XA7jZfdxMFGMgLDPOlmzO2Iw A+E9Uffh6ugR38onUWuj8ewWmeuUDNbwnf2kTf5l7gvzKVHExuo7Gj+LQondaVPU0Ow8 Xb9Cn304TYg8PVsxNtdzR2LaQqk9TOJtOIFDF34bNXHx/Fmih/kjPyzEJYnTuaJtTDtP Cq7DOYxU80cMEHNYAFiOhUZUs8XG2FKbrHMDvrhfOGrKaHJXPj5jI8yxUl/gxcF6Tju9 hHZYZCL8pUvbqijWHbNYzj3Z/1t9us9KK1QnzZW/CEXNnjbjCgGQVbbICF4enmm0c1yY egIg==
X-Received by 10.220.205.195 with SMTP id fr3mr13380807vcb.6.1362688060173; Thu, 07 Mar 2013 12:27:40 -0800 (PST)
MIME-Version 1.0
In-Reply-To <khap77$a95$1@ger.gmane.org>
References <roy-572C99.22201106032013@70-1-84-166.pools.spcsdns.net> <20130306215735.649932ee@bigbox.christie.dr> <loom.20130307T121601-338@post.gmane.org> <CALwzid=wNNBa6Mnx0sr84N1+PiZHMHtra7iQHg_2pYDpsd4kig@mail.gmail.com> <khaep0$qst$1@ger.gmane.org> <CALwzidnpNK7w6gL8Pk1VqBdEFRXUuTdTyyPpOisNeMVpPLuWEg@mail.gmail.com> <khap77$a95$1@ger.gmane.org>
From Ian Kelly <ian.g.kelly@gmail.com>
Date Thu, 7 Mar 2013 13:26:59 -0700
Subject Re: Interesting list() un-optimization
To Python <python-list@python.org>
Content-Type text/plain; charset=ISO-8859-1
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.3051.1362688062.2939.python-list@python.org> (permalink)
Lines 13
NNTP-Posting-Host 2001:888:2000:d::a6
X-Trace 1362688062 news.xs4all.nl 6921 [2001:888:2000:d::a6]:44509
X-Complaints-To abuse@xs4all.nl
Xref csiph.com comp.lang.python:40819

Show key headers only | View raw

On Thu, Mar 7, 2013 at 12:19 PM, Stefan Behnel <stefan_ml@behnel.de> wrote:
>> Didn't know about that, thanks.  Presumably a proper iter(QuerySet())
>> object could implement __length_hint__ in an efficient manner rather
>> than by just calling the __len__ of the underlying QuerySet,
>
> And how exactly would it do that, without either doing what __len__ does or
> reading the whole result set into memory?

If the underlying cursor provides its own efficient length hint, it
could return that.  Or if the query is result-limited, use the limit
as a length hint, provided it's not absurdly large.  And if you really
can't efficiently determine anything about the length of the result
set at all, you can always fall back on returning NotImplemented.

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

Thread

Interesting list() un-optimization Roy Smith <roy@panix.com> - 2013-03-06 22:20 -0500
  Re: Interesting list() un-optimization Dave Angel <davea@davea.name> - 2013-03-06 22:38 -0500
  Re: Interesting list() un-optimization Tim Chase <python.list@tim.thechases.com> - 2013-03-06 21:57 -0600
  Re: Interesting list() un-optimization Kev Dwyer <kevin.p.dwyer@gmail.com> - 2013-03-07 07:31 +0000
  Re: Interesting list() un-optimization Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2013-03-07 11:22 +0000
  Re: Interesting list() un-optimization Ian Kelly <ian.g.kelly@gmail.com> - 2013-03-07 09:00 -0700
  Re: Interesting list() un-optimization Christian Heimes <christian@python.org> - 2013-03-07 17:20 +0100
  Re: Interesting list() un-optimization Ian Kelly <ian.g.kelly@gmail.com> - 2013-03-07 10:31 -0700
  Re: Interesting list() un-optimization Stefan Behnel <stefan_ml@behnel.de> - 2013-03-07 20:19 +0100
  Re: Interesting list() un-optimization Ian Kelly <ian.g.kelly@gmail.com> - 2013-03-07 13:26 -0700
  Re: Interesting list() un-optimization Terry Reedy <tjreedy@udel.edu> - 2013-03-07 15:29 -0500
  Re: Interesting list() un-optimization Terry Reedy <tjreedy@udel.edu> - 2013-03-07 15:34 -0500
  Re: Interesting list() un-optimization Wolfgang Maier <wolfgang.maier@biologie.uni-freiburg.de> - 2013-03-07 20:41 +0000
  Re: Interesting list() un-optimization Terry Reedy <tjreedy@udel.edu> - 2013-03-07 17:53 -0500
  Re: Interesting list() un-optimization Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-08 17:59 +0000
    Re: Interesting list() un-optimization Roy Smith <roy@panix.com> - 2013-03-08 13:45 -0500
  Re: Interesting list() un-optimization Roy Smith <roy@panix.com> - 2013-03-10 09:05 -0400
    Re: Interesting list() un-optimization Terry Reedy <tjreedy@udel.edu> - 2013-03-10 17:39 -0400
      Re: Interesting list() un-optimization Roy Smith <roy@panix.com> - 2013-03-10 18:34 -0400
        Re: Interesting list() un-optimization Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2013-03-10 23:35 +0000
          Re: Interesting list() un-optimization Roy Smith <roy@panix.com> - 2013-03-10 19:50 -0400

csiph-web