Re: Negative array indicies and slice()

From	Roy Smith <roy@panix.com>
Newsgroups	comp.lang.python
Subject	Re: Negative array indicies and slice()
Date	2012-10-29 09:52 -0400
Organization	PANIX Public Access Internet and UNIX, NYC
Message-ID	<roy-F5462C.09525029102012@news.panix.com> (permalink)
References	(2 earlier) <4c024364-84df-403b-8b9e-4a4c8f06121c@googlegroups.com> <mailman.2991.1351484760.27098.python-list@python.org> <cd108b9d-e951-463e-8e50-a5a024a27c7f@googlegroups.com> <508e6649$0$29967$c3e8da3$5496439d@news.astraweb.com> <mailman.3009.1351516065.27098.python-list@python.org>

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In article <mailman.3009.1351516065.27098.python-list@python.org>,
 Andrew Robinson <andrew3@r3dsolutions.com> wrote:

> Show me an example where someone would write a slice with a negative and 
> a positive index (both in the same slice);
> and have that slice grab a contiguous slice in the *middle* of the list 
> with orientation of lower index to greater index.

It's possible in bioinformatics.  Many organisms have circular 
chromosomes.  It's a single DNA molecule spliced into a loop.  There's 
an "origin", but it's more a convenience thing for people to assign some 
particular base-pair to be location 0.  From the organism's point of 
view, the origin isn't anything special (but there *is* a fixed 
orientation).

It's entirely plausible for somebody to want to extract the sub-sequence 
from 100 bp (base-pairs) before the origin to 100 bp after the origin.  
If you were storing the sequence in Python string (or list), the most 
convenient way to express this would be seq[-100:100].  Likewise, if you 
wanted the *other* fragment, you would write seq[100:-100].

There is a minor confounding factor here in that biologists number 
sequences starting with 1, not 0.  At least that was the way when I was 
doing this stuff mumble years ago.  I don't know what the current 
convention is.

Thread

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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