Re: Multi-dimensional list initialization

Newsgroups	comp.lang.python
Date	2012-11-09 07:05 -0800
References	(7 earlier) <mailman.3343.1352242047.27098.python-list@python.org> <5099bf7d$0$29980$c3e8da3$5496439d@news.astraweb.com> <k7hmtd$sev$1@ger.gmane.org> <mailman.3475.1352441232.27098.python-list@python.org> <509ca4b5$0$29980$c3e8da3$5496439d@news.astraweb.com>
Message-ID	<ef8a7756-73fb-4693-97fb-24778360a91c@vy11g2000pbb.googlegroups.com> (permalink)
Subject	Re: Multi-dimensional list initialization
From	rusi <rustompmody@gmail.com>

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On Nov 9, 11:37 am, Steven D'Aprano <steve
+comp.lang.pyt...@pearwood.info> wrote:
> On Fri, 09 Nov 2012 17:07:09 +1100, Chris Angelico wrote:
> > On Fri, Nov 9, 2012 at 12:39 PM, Mark Lawrence <breamore...@yahoo.co.uk>
> > wrote:
> >> On 07/11/2012 01:55, Steven D'Aprano wrote:
>
> >>> Who knows? Who cares? Nobody does:
>
> >>> n -= n
>
> >> But I've seen this scattered through code:
>
> >> x := x - x - x
>
> > Can you enlighten us as to how this is better than either:
> >  x := -x
> > or
> >  x := 0 - x
> > ? I'm not seeing it.
>
> I'm hoping that Mark intended it as an example of crappy code he has
> spotted in some other language rather than a counter-example of something
> you would do.
>
> To be pedantic... there may very well be some (rare) cases where you
> actually do want x -= x rather than just x = 0. Consider the case where x
> could be an INF or NAN. Then x -= x should give x = NAN rather than zero.
> That may be desirable in some cases.

In x86 assembler
mov ax, 0
is 4 bytes
sub ax, ax
is 2
and therefore better (at least for those brought up on Peter Norton);
the most common being
xor ax, ax

Thread

Multi-dimensional list initialization Demian Brecht <demianbrecht@gmail.com> - 2012-11-04 22:27 -0800
  Re: Multi-dimensional list initialization Hans Mulder <hansmu@xs4all.nl> - 2012-11-05 10:13 +0100
    Re: Multi-dimensional list initialization Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-11-06 01:32 +0000
    Re: Multi-dimensional list initialization Chris Angelico <rosuav@gmail.com> - 2012-11-06 13:01 +1100
    Re: Multi-dimensional list initialization Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-11-06 02:30 +0000
    Re: Multi-dimensional list initialization Andrew Robinson <andrew3@r3dsolutions.com> - 2012-11-05 21:51 -0800
      Re: Multi-dimensional list initialization Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-06 09:04 +0000
        RE: Multi-dimensional list initialization "Shambhu Rajak" <shambhu.rajak@calsoftinc.com> - 2012-11-06 18:57 +0530
        Re: Multi-dimensional list initialization Andrew Robinson <andrew3@r3dsolutions.com> - 2012-11-06 14:41 -0800
          Re: Multi-dimensional list initialization Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-07 01:55 +0000
            Re: Multi-dimensional list initialization Demian Brecht <demianbrecht@gmail.com> - 2012-11-06 22:56 -0800
            Re: Multi-dimensional list initialization wxjmfauth@gmail.com - 2012-11-07 00:57 -0800
            Re: Multi-dimensional list initialization Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-11-07 22:27 +0000
            Re: Multi-dimensional list initialization Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-07 16:39 -0700
            Re: Multi-dimensional list initialization Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-08 00:09 -0700
            Re: Multi-dimensional list initialization Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-08 08:58 -0700
            Re: Multi-dimensional list initialization Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-11-09 01:39 +0000
            Re: Multi-dimensional list initialization Chris Angelico <rosuav@gmail.com> - 2012-11-09 17:07 +1100
              Re: Multi-dimensional list initialization Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-09 06:37 +0000
                Re: Multi-dimensional list initialization Chris Angelico <rosuav@gmail.com> - 2012-11-09 17:59 +1100
                Re: Multi-dimensional list initialization Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-11-09 07:27 +0000
                Re: Multi-dimensional list initialization rusi <rustompmody@gmail.com> - 2012-11-09 07:05 -0800
                Re: Multi-dimensional list initialization Chris Angelico <rosuav@gmail.com> - 2012-11-10 02:23 +1100
            Re: Multi-dimensional list initialization Dennis Lee Bieber <wlfraed@ix.netcom.com> - 2012-11-09 14:34 -0500
            RE: Multi-dimensional list initialization "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2012-11-09 20:31 +0000
            Re: Multi-dimensional list initialization Ethan Furman <ethan@stoneleaf.us> - 2012-11-09 13:49 -0800
        RE: Multi-dimensional list initialization "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2012-11-06 23:39 +0000
        Re: Multi-dimensional list initialization Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-06 16:52 -0700
        Re: Multi-dimensional list initialization MRAB <python@mrabarnett.plus.com> - 2012-11-07 00:23 +0000
          Re: Multi-dimensional list initialization rusi <rustompmody@gmail.com> - 2012-11-06 20:11 -0800
          Re: Multi-dimensional list initialization Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-07 05:05 +0000
            Re: Multi-dimensional list initialization Roy Smith <roy@panix.com> - 2012-11-07 00:12 -0500
              Re: Multi-dimensional list initialization Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2012-11-07 18:32 +1300
                RE: Multi-dimensional list initialization "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2012-11-07 15:57 +0000
            Re: Multi-dimensional list initialization Jussi Piitulainen <jpiitula@ling.helsinki.fi> - 2012-11-07 10:52 +0200
            Re: Multi-dimensional list initialization MRAB <python@mrabarnett.plus.com> - 2012-11-07 17:17 +0000
              Re: Multi-dimensional list initialization Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-07 22:36 +0000
        Re: Multi-dimensional list initialization Ethan Furman <ethan@stoneleaf.us> - 2012-11-07 07:23 -0800
        Re: Multi-dimensional list initialization Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-07 14:01 -0700
          Re: Multi-dimensional list initialization Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-08 00:00 +0000
            Re: Multi-dimensional list initialization Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-11-08 00:30 +0000
              Re: Multi-dimensional list initialization Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-08 03:47 +0000
            Re: Multi-dimensional list initialization Andrew Robinson <andrew3@r3dsolutions.com> - 2012-11-07 20:51 -0800
            Re: Multi-dimensional list initialization wrw@mac.com - 2012-11-08 08:26 -0500
        Re: Multi-dimensional list initialization Andrew Robinson <andrew3@r3dsolutions.com> - 2012-11-07 16:24 -0800
          Re: Multi-dimensional list initialization Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-11-08 04:20 +0000
    Re: Multi-dimensional list initialization Chris Angelico <rosuav@gmail.com> - 2012-11-06 17:07 +1100
    Re: Multi-dimensional list initialization Andrew Robinson <andrew3@r3dsolutions.com> - 2012-11-06 00:21 -0800
    Re: Multi-dimensional list initialization Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-06 02:19 -0700
    RE: Multi-dimensional list initialization "Prasad, Ramit" <ramit.prasad@jpmorgan.com> - 2012-11-06 17:32 +0000
    Re: Multi-dimensional list initialization Andrew Robinson <andrew3@r3dsolutions.com> - 2012-11-06 13:14 -0800
    Re: Multi-dimensional list initialization Andrew Robinson <andrew3@r3dsolutions.com> - 2012-11-06 13:19 -0800
    Re: Multi-dimensional list initialization Ian Kelly <ian.g.kelly@gmail.com> - 2012-11-06 15:46 -0700
      Re: Multi-dimensional list initialization Gregory Ewing <greg.ewing@canterbury.ac.nz> - 2012-11-07 18:34 +1300
        Re: Multi-dimensional list initialization Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-11-07 14:00 +0000
        Re: Multi-dimensional list initialization Ethan Furman <ethan@stoneleaf.us> - 2012-11-07 06:47 -0800
        Re: Multi-dimensional list initialization Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-11-07 23:06 +0000
        Re: Multi-dimensional list initialization Greg Ewing <greg.ewing@canterbury.ac.nz> - 2012-11-08 14:29 +1300
  Re: Multi-dimensional list initialization wxjmfauth@gmail.com - 2012-11-05 01:55 -0800

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