Groups > comp.lang.python > #11924

Re: extended slicing and negative stop value problem

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Date	Sat, 20 Aug 2011 19:29:42 +0100
Subject	Re: extended slicing and negative stop value problem
From	Chris Angelico <rosuav@gmail.com>
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On Sat, Aug 20, 2011 at 7:20 PM, Max Moroz <maxmoroz@gmail.com> wrote:
> Would it be a good idea to change Python definition so that a[10, -1, -1]
> referred to the elements starting with position 10, going down to the
> beginning?

Well, first off I think it's a dangerous idea to change semantics of
something like that. I can see your use case, but I think that what
you want is covered by simply omitting the stop marker:

>>> a="qwertyuiopasdfghjklzxcvbnm"
>>> a[10:1:-1]
'apoiuytre'
>>> a[10:0:-1]
'apoiuytrew'
>>> a[10::-1]
'apoiuytrewq'

If you're using a variable for the stop value, you just need to set it
to an explicit None if it would fall negative:

>>> a[10:None:-1]
'apoiuytrewq'

Hope that helps!

ChrisA

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Thread

Re: extended slicing and negative stop value problem Chris Angelico <rosuav@gmail.com> - 2011-08-20 19:29 +0100
  Re: extended slicing and negative stop value problem Max <maxmoroz@gmail.com> - 2011-08-20 11:52 -0700
    Re: extended slicing and negative stop value problem Chris Angelico <rosuav@gmail.com> - 2011-08-20 20:53 +0100
  Re: extended slicing and negative stop value problem Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-08-21 06:40 +1000
    Re: extended slicing and negative stop value problem Max <maxmoroz@gmail.com> - 2011-08-21 10:27 -0700
      Re: extended slicing and negative stop value problem Chris Rebert <clp2@rebertia.com> - 2011-08-21 15:16 -0700

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