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Re: is implemented with id ?

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Date Sun, 4 Nov 2012 01:14:29 +0000
Subject Re: is implemented with id ?
From Oscar Benjamin <oscar.j.benjamin@gmail.com>
To Chris Angelico <rosuav@gmail.com>
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On 3 November 2012 22:50, Chris Angelico <rosuav@gmail.com> wrote:
> This one I haven't checked the source for, but ISTR discussions on
> this list about comparison of two unequal interned strings not being
> optimized, so they'll end up being compared char-for-char. Using 'is'
> guarantees that the check stops with identity. This may or may not be
> significant, and as you say, defending against an uninterned string
> slipping through is potentially critical.

The source is here (and it shows what you suggest):
http://hg.python.org/cpython/file/6c639a1ff53d/Objects/unicodeobject.c#l6128

Comparing strings char for char is really not that big a deal though.
This has been discussed before: you don't need to compare very many
characters to conclude that strings are unequal (if I remember
correctly you were part of that discussion).

I can imagine cases where I might consider using intern on lots of
strings to speed up comparisons but I would have to be involved in
some seriously heavy and obscure string processing problem before I
considered using 'is' to compare those interned strings. That is
confusing to anyone who reads the code, prone to bugs and unlikely to
achieve the desired outcome of speeding things up (noticeably).


Oscar

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Thread

is implemented with id ? Franck Ditter <franck@ditter.org> - 2012-09-05 08:30 +0200
  Re: is implemented with id ? Benjamin Kaplan <benjamin.kaplan@case.edu> - 2012-09-04 23:40 -0700
    Re: is implemented with id ? Franck Ditter <franck@ditter.org> - 2012-09-05 15:19 +0200
      Re: is implemented with id ? Hans Mulder <hansmu@xs4all.nl> - 2012-09-05 15:48 +0200
        Re: is implemented with id ? aahz@pythoncraft.com (Aahz) - 2012-11-03 12:41 -0700
          Re: is implemented with id ? Hans Mulder <hansmu@xs4all.nl> - 2012-11-03 22:49 +0100
            Re: is implemented with id ? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-03 22:18 +0000
              Re: is implemented with id ? Chris Angelico <rosuav@gmail.com> - 2012-11-04 09:50 +1100
              Re: is implemented with id ? Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-11-04 01:14 +0000
                Re: is implemented with id ? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-04 03:10 +0000
                Re: is implemented with id ? Chris Angelico <rosuav@gmail.com> - 2012-11-04 14:19 +1100
                Re: is implemented with id ? aahz@pythoncraft.com (Aahz) - 2012-11-03 22:09 -0700
                Re: is implemented with id ? Hans Mulder <hansmu@xs4all.nl> - 2012-11-04 11:13 +0100
              Re: is implemented with id ? Chris Angelico <rosuav@gmail.com> - 2012-11-04 12:22 +1100
              Re: is implemented with id ? aahz@pythoncraft.com (Aahz) - 2012-11-03 22:08 -0700
            Re: is implemented with id ? Roy Smith <roy@panix.com> - 2012-11-03 18:41 -0400
            Re: is implemented with id ? aahz@pythoncraft.com (Aahz) - 2012-11-03 22:12 -0700
      Re: is implemented with id ? Dave Angel <d@davea.name> - 2012-09-05 10:00 -0400
        Re: is implemented with id ? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-05 14:41 +0000
          Re: is implemented with id ? Dave Angel <d@davea.name> - 2012-09-05 11:09 -0400
            Re: is implemented with id ? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-05 15:36 +0000
            Re: is implemented with id ? Hans Mulder <hansmu@xs4all.nl> - 2012-09-05 18:47 +0200
              Re: is implemented with id ? Dave Angel <d@davea.name> - 2012-09-05 13:19 -0400
          Re: is implemented with id ? Terry Reedy <tjreedy@udel.edu> - 2012-09-05 14:31 -0400
          Re: is implemented with id ? Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-09-05 22:08 -0400
          Re: is implemented with id ? Duncan Booth <duncan.booth@invalid.invalid> - 2012-09-06 09:34 +0000
            Re: is implemented with id ? Chris Angelico <rosuav@gmail.com> - 2012-09-06 19:50 +1000
          Re: is implemented with id ? 88888 Dihedral <dihedral88888@googlemail.com> - 2012-11-04 01:33 -0700
  Re: is implemented with id ? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-05 09:14 +0000
    Re: is implemented with id ? Ramchandra Apte <maniandram01@gmail.com> - 2012-09-05 05:48 -0700
      Re: is implemented with id ? Dave Angel <d@davea.name> - 2012-09-05 09:46 -0400
      Re: is implemented with id ? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-05 14:13 +0000
        Re: is implemented with id ? Ian Kelly <ian.g.kelly@gmail.com> - 2012-09-05 11:08 -0600
        Re: is implemented with id ? Chris Angelico <rosuav@gmail.com> - 2012-09-06 19:07 +1000
      Re: is implemented with id ? Terry Reedy <tjreedy@udel.edu> - 2012-09-05 14:27 -0400
        Re: is implemented with id ? Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-09-06 06:44 +0000
          Re: is implemented with id ? Ramchandra Apte <maniandram01@gmail.com> - 2012-09-06 01:24 -0700
          Re: is implemented with id ? Roy Smith <roy@panix.com> - 2012-09-06 08:16 -0400
            Re: is implemented with id ? Ramchandra Apte <maniandram01@gmail.com> - 2012-09-06 06:30 -0700
      Re: is implemented with id ? Dave Angel <d@davea.name> - 2012-09-05 14:40 -0400

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