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Groups > comp.lang.python > #5873

Re: hash values and equality

From Christian Heimes <lists@cheimes.de>
Subject Re: hash values and equality
Date 2011-05-20 21:01 +0200
References (5 earlier) <BANLkTikx8U4jWwLXXazpmtsL6MasDmyVyg@mail.gmail.com> <BANLkTi=_GqrNntRU7pv7x=kj3gHurk-Gaw@mail.gmail.com> <mailman.1822.1305870290.9059.python-list@python.org> <0deha8-6u9.ln1@satorlaser.homedns.org> <4DD68DAA.9050209@mrabarnett.plus.com>
Newsgroups comp.lang.python
Message-ID <mailman.1855.1305918095.9059.python-list@python.org> (permalink)

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Am 20.05.2011 17:50, schrieb MRAB:
> Is this strictly true? I thought that the hash value, an integer, is
> moduloed (Is that how you spell it? Looks weird!) with the number of
> array elements to give an index into the array, so different hashes
> could give the same index, and objects with different hashes could be
> stored in the same 'bucket'.

I don't think 'moduloed' is an existing word but your description is
mostly correct. The hash of the object and length of the hash table are
used to calculate the position in the hash table. However Python's
implementation doesn't use buckets to reduce memory usage and pointer
dereferencing. If a slot in the hash table is already filled with an
object that is not equal to the new object (a collision), the hash is
shifted and the new slot is checked. The implementation detail is well
described in Modules/dictobject.c.

Christian

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Thread

hash values and equality Ethan Furman <ethan@stoneleaf.us> - 2011-05-19 22:43 -0700
  Re: hash values and equality Peter Otten <__peter__@web.de> - 2011-05-20 08:38 +0200
    Re: hash values and equality Ethan Furman <ethan@stoneleaf.us> - 2011-05-20 10:57 -0700
    Re: hash values and equality Peter Otten <__peter__@web.de> - 2011-05-20 22:25 +0200
    Re: hash values and equality Ethan Furman <ethan@stoneleaf.us> - 2011-05-20 14:48 -0700
  Re: hash values and equality Ulrich Eckhardt <ulrich.eckhardt@dominolaser.com> - 2011-05-20 08:33 +0200
    Re: hash values and equality MRAB <python@mrabarnett.plus.com> - 2011-05-20 16:50 +0100
    Re: hash values and equality Chris Angelico <rosuav@gmail.com> - 2011-05-21 02:20 +1000
    Re: hash values and equality Ian Kelly <ian.g.kelly@gmail.com> - 2011-05-20 11:59 -0600
    Re: hash values and equality Ethan Furman <ethan@stoneleaf.us> - 2011-05-20 11:38 -0700
      Re: hash values and equality Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2011-05-21 20:24 +1200
        Re: hash values and equality Peter Otten <__peter__@web.de> - 2011-05-21 11:24 +0200
    Re: hash values and equality Christian Heimes <lists@cheimes.de> - 2011-05-20 21:01 +0200
    Re: hash values and equality MRAB <python@mrabarnett.plus.com> - 2011-05-20 21:17 +0100
      Re: hash values and equality Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-21 00:47 +0000
        Re: hash values and equality MRAB <python@mrabarnett.plus.com> - 2011-05-21 02:02 +0100
          Re: hash values and equality Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-21 01:55 +0000
    Re: hash values and equality John Nagle <nagle@animats.com> - 2011-05-21 15:55 -0700
      Re: hash values and equality Irmen de Jong <irmen.NOSPAM@xs4all.nl> - 2011-05-22 01:07 +0200
      Re: hash values and equality Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-05-22 00:24 +0000

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