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Re: order independent hash?

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Date Sun, 04 Dec 2011 12:57:50 -0600
From Tim Chase <python.list@tim.thechases.com>
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Subject Re: order independent hash?
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On 12/04/11 08:08, Chris Angelico wrote:
> 2011/12/5 Hrvoje Niksic<hniksic@xemacs.org>:
>> If a Python
>> implementation tried to implement dict as a tree, instances of classes
>> that define only __eq__ and __hash__ would not be correctly inserted in
>> such a dict.
>
> Couldn't you just make a tree of hash values? Okay, that's probably
> not the most useful way to do things, but technically it'd comply with
> the spec.

 From an interface perspective, I suppose it would work.  However 
one of the main computer-science reasons for addressing by a hash 
is to get O(1) access to items (modulo pessimal hash 
structures/algorithms which can approach O(N) if everything 
hashes to the same value/bucket), rather than the O(logN) time 
you'd get from a tree. So folks reaching for a hash/map might be 
surprised if performance degraded with the size of the contents.

-tkc

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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

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