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

Groups > comp.lang.python > #16572

Re: order independent hash?

Path csiph.com!x330-a1.tempe.blueboxinc.net!usenet.pasdenom.info!gegeweb.org!de-l.enfer-du-nord.net!feeder1.enfer-du-nord.net!feeds.phibee-telecom.net!newsfeed.xs4all.nl!newsfeed6.news.xs4all.nl!xs4all!post.news.xs4all.nl!not-for-mail
Return-Path <python-python-list@m.gmane.org>
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; 'received:verizon.net': 0.07; 'terry': 0.07; 'contexts': 0.09; 'dict': 0.09; 'mutable': 0.09; 'received:80.91': 0.09; 'received:80.91.229': 0.09; 'received:80.91.229.12': 0.09; 'received:gmane.org': 0.09; 'received:list': 0.09; 'received:lo.gmane.org': 0.09; 'am,': 0.12; '"python': 0.15; 'additions': 0.16; 'deletions': 0.16; 'does,': 0.16; 'hashable': 0.16; 'reedy': 0.16; 'subject:independent': 0.16; 'wrote:': 0.18; '>>>': 0.18; 'perl': 0.18; 'purposes,': 0.18; 'jan': 0.19; 'memory': 0.21; 'mechanism': 0.21; 'header:In- Reply-To:1': 0.22; 'table.': 0.23; 'tree': 0.25; 'writes:': 0.25; 'structure': 0.26; '(this': 0.28; 'mapping': 0.29; 'seem': 0.30; 'hash': 0.30; 'protocol.': 0.30; '\xe2\x80\x94': 0.30; 'chris': 0.30; 'equivalent': 0.31; 'subject:?': 0.31; 'does': 0.32; 'values': 0.32; 'programmers': 0.32; 'pretty': 0.32; "isn't": 0.33; 'header:User-Agent:1': 0.33; 'header:X-Complaints-To:1': 0.33; 'instead': 0.33; 'there': 0.33; 'object': 0.33; 'to:addr :python-list': 0.34; 'especially': 0.35; 'but': 0.37; 'run': 0.37; 'could': 0.37; 'maps': 0.38; 'received:org': 0.38; 'tables': 0.39; 'called': 0.40; "it's": 0.40; 'to:addr:python.org': 0.40; 'management': 0.60; 'types': 0.61; 'grow': 0.62; 'auto': 0.63
X-Injected-Via-Gmane http://gmane.org/
To python-list@python.org
From Terry Reedy <tjreedy@udel.edu>
Subject Re: order independent hash?
Date Fri, 02 Dec 2011 16:40:24 -0500
References <jb57p7$b1j$1@dough.gmane.org> <mailman.3156.1322657239.27778.python-list@python.org> <30715729.411.1322753732534.JavaMail.geo-discussion-forums@pret21> <4ED7A2CE.6070306@davea.name> <mailman.3203.1322756312.27778.python-list@python.org> <6366868.86.1322800180523.JavaMail.geo-discussion-forums@pret21> <mailman.3216.1322802013.27778.python-list@python.org> <87k46fb8pg.fsf@xemacs.org>
Mime-Version 1.0
Content-Type text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding quoted-printable
X-Gmane-NNTP-Posting-Host pool-74-109-121-73.phlapa.fios.verizon.net
User-Agent Mozilla/5.0 (Windows NT 6.1; WOW64; rv:8.0) Gecko/20111105 Thunderbird/8.0
In-Reply-To <87k46fb8pg.fsf@xemacs.org>
X-BeenThere python-list@python.org
X-Mailman-Version 2.1.12
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.3239.1322862043.27778.python-list@python.org> (permalink)
Lines 36
NNTP-Posting-Host 2001:888:2000:d::a6
X-Trace 1322862043 news.xs4all.nl 6904 [2001:888:2000:d::a6]:47937
X-Complaints-To abuse@xs4all.nl
Xref x330-a1.tempe.blueboxinc.net comp.lang.python:16572

Show key headers only | View raw

On 12/2/2011 4:53 AM, Hrvoje Niksic wrote:
> Chris Angelico<rosuav@gmail.com>  writes:
>
>>> The hash can grow with (k,v) pairs accumulated in the run time.
>>> An auto memory management mechanism is required for a hash of a non-fixed size of (k,v) pairs.
>>
>> That's a hash table
>
> In many contexts "hash table" is shortened to "hash" when there is no
> ambiguity.  This is especially popular among Perl programmers where the
> equivalent of dict is called a hash.
>
>> Although strictly speaking, isn't that "Python dicts are implemented
>> as hash tables in CPython"? Or is the hashtable implementation
>> mandated?
>
> It's pretty much mandated because of the __hash__ protocol.

Lib Ref 4.8. Mapping Types — dict
"A mapping object maps hashable values to arbitrary objects."

This does not say that the mapping has to *use* the hash value ;-).
Even if it does, it could use a tree structure instead of a hash table. 
But hash tables seem to work well for general purposes,

"Mappings are mutable objects."
(This would change if a frozendict were added.)

especially when additions and deletions are needed.

-- 
Terry Jan Reedy

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

Thread

Re: order independent hash? Peter Otten <__peter__@web.de> - 2011-11-30 13:47 +0100
  Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-01 07:35 -0800
  Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-01 07:35 -0800
    Re: order independent hash? Dave Angel <d@davea.name> - 2011-12-01 10:52 -0500
      Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-01 08:17 -0800
      Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-01 08:17 -0800
    Re: order independent hash? Chris Angelico <rosuav@gmail.com> - 2011-12-02 03:18 +1100
      Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-01 20:29 -0800
        Re: order independent hash? Chris Angelico <rosuav@gmail.com> - 2011-12-02 16:00 +1100
          Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-01 21:48 -0800
            Re: order independent hash? Lie Ryan <lie.1296@gmail.com> - 2011-12-05 00:40 +1100
          Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-01 21:48 -0800
            Re: order independent hash? Roel Schroeven <rschroev_nospam_ml@fastmail.fm> - 2011-12-04 14:41 +0100
              Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-04 07:39 -0800
                Re: order independent hash? Ian Kelly <ian.g.kelly@gmail.com> - 2011-12-04 10:41 -0700
                Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-04 10:06 -0800
                Re: order independent hash? Ian Kelly <ian.g.kelly@gmail.com> - 2011-12-04 13:13 -0700
                Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-04 15:17 -0800
                Re: order independent hash? Matt Joiner <anacrolix@gmail.com> - 2011-12-05 10:21 +1100
                Re: order independent hash? Ian Kelly <ian.g.kelly@gmail.com> - 2011-12-04 16:24 -0700
                Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-04 16:52 -0800
                Re: order independent hash? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-05 02:00 +0000
                Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-04 16:52 -0800
                Re: order independent hash? Lie Ryan <lie.1296@gmail.com> - 2011-12-05 12:59 +1100
                Re: order independent hash? Ethan Furman <ethan@stoneleaf.us> - 2011-12-04 18:08 -0800
                Re: order independent hash? Ben Finney <ben+python@benfinney.id.au> - 2011-12-05 15:52 +1100
                Re: order independent hash? Matt Joiner <anacrolix@gmail.com> - 2011-12-05 14:02 +1100
                Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-06 21:24 -0800
                Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-06 21:24 -0800
                Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-04 15:17 -0800
                Re: order independent hash? Terry Reedy <tjreedy@udel.edu> - 2011-12-04 19:28 -0500
                Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-04 10:06 -0800
          Re: order independent hash? Hrvoje Niksic <hniksic@xemacs.org> - 2011-12-02 10:53 +0100
            Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-02 03:48 -0800
            Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-02 09:00 -0800
            Re: order independent hash? Terry Reedy <tjreedy@udel.edu> - 2011-12-02 16:40 -0500
              Re: order independent hash? Hrvoje Niksic <hniksic@xemacs.org> - 2011-12-04 14:55 +0100
                Re: order independent hash? Chris Angelico <rosuav@gmail.com> - 2011-12-05 01:08 +1100
                Re: order independent hash? Hrvoje Niksic <hniksic@xemacs.org> - 2011-12-07 14:28 +0100
                Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-07 09:48 -0800
                Re: order independent hash? Tim Chase <python.list@tim.thechases.com> - 2011-12-04 12:57 -0600
                Re: order independent hash? Hrvoje Niksic <hniksic@xemacs.org> - 2011-12-08 10:30 +0100
                Re: order independent hash? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-09 11:27 +0000
                Re: order independent hash? Hrvoje Niksic <hniksic@xemacs.org> - 2011-12-09 17:51 +0100
                Re: order independent hash? Chris Angelico <rosuav@gmail.com> - 2011-12-10 04:13 +1100
                Re: order independent hash? Lie Ryan <lie.1296@gmail.com> - 2011-12-11 10:58 +1100
                Re: order independent hash? Chris Angelico <rosuav@gmail.com> - 2011-12-11 11:17 +1100
                Re: order independent hash? Lie Ryan <lie.1296@gmail.com> - 2011-12-11 14:04 +1100
        Re: order independent hash? Lie Ryan <lie.1296@gmail.com> - 2011-12-05 00:29 +1100
      Re: order independent hash? 88888 Dihedral <dihedral88888@googlemail.com> - 2011-12-01 20:29 -0800
      Re: order independent hash? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-12-02 04:33 +0000

csiph-web