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Re: Negative array indicies and slice()

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From Ian Kelly <ian.g.kelly@gmail.com>
Date Sun, 28 Oct 2012 21:42:50 -0600
Subject Re: Negative array indicies and slice()
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On Sun, Oct 28, 2012 at 9:12 PM,  <andrewr3mail@gmail.com> wrote:
> The slice operator does not give any way (I can find!) to take slices from negative to positive indexes, although the range is not empty, nor the expected indexes out of range that I am supplying.
>
> Many programs that I write would require introducing variables and logical statements to correct the problem which is very lengthy and error prone unless there is a simple work around.
>
> I *hate* replicating code every time I need to do this!
>
> I also don't understand why slice() is not equivalent to an iterator, but can replace an integer in __getitem__() whereas xrange() can't.
>
>
> Here's an example for Linux shell, otherwise remove /bin/env...
> {{{#!/bin/env python
> a=[1,2,3,4,5,6,7,8,9,10]
> print a[-4:3]  # I am interested in getting [7,8,9,10,1,2] but I get [].
> }}}


For a sequence of length 10, "a[-4:3]" is equivalent to "a[6:3]",
which is an empty slice since index 6 is after index 3.

If you want it to wrap around, then take two slices and concatenate
them with "a[-4:] + a[:3]".

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Negative array indicies and slice() andrewr3mail@gmail.com - 2012-10-28 20:12 -0700
  Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-28 21:42 -0600
    Re: Negative array indicies and slice() andrewr3mail@gmail.com - 2012-10-28 21:00 -0700
      Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-28 22:25 -0600
        Re: Negative array indicies and slice() Andrew <andrewr3mail@gmail.com> - 2012-10-29 00:54 -0700
          Re: Negative array indicies and slice() Chris Rebert <clp2@rebertia.com> - 2012-10-29 01:18 -0700
          Re: Negative array indicies and slice() Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-10-29 11:19 +0000
            Re: Negative array indicies and slice() Chris Angelico <rosuav@gmail.com> - 2012-10-29 22:32 +1100
            Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-28 21:52 -0700
            Re: Negative array indicies and slice() Chris Angelico <rosuav@gmail.com> - 2012-10-29 23:40 +1100
              Re: Negative array indicies and slice() Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-10-29 22:02 +0000
            Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-28 23:01 -0700
              Re: Negative array indicies and slice() Roy Smith <roy@panix.com> - 2012-10-29 09:52 -0400
                Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-29 08:20 -0700
                Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-29 17:01 -0600
                Re: Negative array indicies and slice() Oscar Benjamin <oscar.j.benjamin@gmail.com> - 2012-10-30 00:04 +0000
                Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-29 16:54 -0700
                Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-30 02:15 -0600
            Re: Negative array indicies and slice() Chris Angelico <rosuav@gmail.com> - 2012-10-30 00:53 +1100
            Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-29 11:09 -0600
            Re: Negative array indicies and slice() Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-10-29 22:14 +0000
            Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-29 08:42 -0700
              Re: Negative array indicies and slice() Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-10-30 00:02 +0000
                Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-29 12:34 -0700
                Re: Negative array indicies and slice() Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-10-30 08:17 +0000
                Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-30 08:47 -0700
                Re: Negative array indicies and slice() Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-10-30 23:48 +0000
                Re: Negative array indicies and slice() Michael Torrie <torriem@gmail.com> - 2012-10-30 23:29 -0600
                Re: Negative array indicies and slice() Michael Torrie <torriem@gmail.com> - 2012-10-29 23:53 -0600
                Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-29 17:04 -0700
            Re: Negative array indicies and slice() Chris Angelico <rosuav@gmail.com> - 2012-10-30 09:55 +1100
            Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-29 17:07 -0600
              Re: Negative array indicies and slice() Roy Smith <roy@panix.com> - 2012-10-29 19:24 -0400
                Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-29 17:43 -0600
                Re: Negative array indicies and slice() Roy Smith <roy@panix.com> - 2012-10-29 20:17 -0400
                Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-29 18:05 -0600
            Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-29 11:00 -0700
            Re: Negative array indicies and slice() Chris Kaynor <ckaynor@zindagigames.com> - 2012-10-29 18:49 -0700
            Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-29 15:39 -0700
            Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-29 23:55 -0600
            Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-30 00:51 -0600
            Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-29 17:17 -0700
            Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-30 01:21 -0600
            Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-30 01:32 -0600
            Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-30 02:46 -0600
            Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-30 12:02 -0600
            Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-30 07:21 -0700
            Re: Negative array indicies and slice() Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-10-30 21:33 +0000
              Re: Negative array indicies and slice() Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-10-31 10:07 +0000
                Re: Negative array indicies and slice() Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-10-31 16:01 +0000
            Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-30 15:47 -0600
            Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-30 15:55 -0600
            Re: Negative array indicies and slice() Chris Angelico <rosuav@gmail.com> - 2012-10-31 09:00 +1100
            Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-30 16:02 -0600
            Re: Negative array indicies and slice() Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-10-30 23:30 +0000
          Re: Negative array indicies and slice() Ian Kelly <ian.g.kelly@gmail.com> - 2012-10-29 11:27 -0600
          Re: Negative array indicies and slice() Andrew Robinson <andrew3@r3dsolutions.com> - 2012-10-29 16:33 -0700
        Re: Negative array indicies and slice() Andrew <andrewr3mail@gmail.com> - 2012-10-29 00:54 -0700
    Re: Negative array indicies and slice() andrewr3mail@gmail.com - 2012-10-28 21:00 -0700
    Re: Negative array indicies and slice() Andrew <andrewr3mail@gmail.com> - 2012-10-28 21:09 -0700
      Re: Negative array indicies and slice() alex23 <wuwei23@gmail.com> - 2012-10-28 21:44 -0700
        Re: Negative array indicies and slice() andrewr3mail@gmail.com - 2012-10-29 01:24 -0700
          Re: Negative array indicies and slice() Chris Rebert <clp2@rebertia.com> - 2012-10-29 01:37 -0700
            Re: Negative array indicies and slice() andrewr3mail@gmail.com - 2012-10-29 01:59 -0700
              Re: Negative array indicies and slice() Mark Lawrence <breamoreboy@yahoo.co.uk> - 2012-10-29 09:36 +0000
              Re: Negative array indicies and slice() Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2012-10-29 10:34 +0000
            Re: Negative array indicies and slice() andrewr3mail@gmail.com - 2012-10-29 01:59 -0700
      Re: Negative array indicies and slice() Paul Rubin <no.email@nospam.invalid> - 2012-10-28 22:14 -0700
        Re: Negative array indicies and slice() andrewr3mail@gmail.com - 2012-10-29 01:08 -0700
          Re: Negative array indicies and slice() Chris Rebert <clp2@rebertia.com> - 2012-10-29 01:26 -0700
    Re: Negative array indicies and slice() Andrew <andrewr3mail@gmail.com> - 2012-10-28 21:09 -0700
  Re: Negative array indicies and slice() MRAB <python@mrabarnett.plus.com> - 2012-10-29 03:45 +0000
  Re: Negative array indicies and slice() 88888 Dihedral <dihedral88888@googlemail.com> - 2012-11-01 18:08 -0700

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