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Groups > comp.lang.python > #103999

Re: list reversal error

From John Gordon <gordon@panix.com>
Newsgroups comp.lang.python
Subject Re: list reversal error
Date 2016-03-03 23:08 +0000
Organization PANIX Public Access Internet and UNIX, NYC
Message-ID <nbag4v$vs$1@reader1.panix.com> (permalink)
References <8b3d06eb-0027-4396-bdf8-fee0cc9ff771@googlegroups.com>

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In <8b3d06eb-0027-4396-bdf8-fee0cc9ff771@googlegroups.com> vlyamtsev@gmail.com writes:

> i have list of strings "data" and i am trying to build reverse list data1
> data1 = []
> for i in range(len(data)):
>    j = len(data) - i
>    data1.append(data[j])

> but i have the following error:
> data1.append(data[j])
> IndexError: list index out of range
>  
> am i doing it wrong?
> Thanks

Python lists are zero-indexed, meaning a list of five items will have
indexes 0 to 4.

The first time through your loop, i is 0, so

    j = len(data) - i 

evaluates to

    j = len(data)

which would yield 5 for a five-element list, but the last actual element
is in data[4].

-- 
John Gordon                   A is for Amy, who fell down the stairs
gordon@panix.com              B is for Basil, assaulted by bears
                                -- Edward Gorey, "The Gashlycrumb Tinies"

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Thread

list reversal error vlyamtsev@gmail.com - 2016-03-03 14:51 -0800
  Re: list reversal error John Gordon <gordon@panix.com> - 2016-03-03 23:08 +0000
    Re: list reversal error Joel Goldstick <joel.goldstick@gmail.com> - 2016-03-03 18:13 -0500
    Re: list reversal error MRAB <python@mrabarnett.plus.com> - 2016-03-03 23:20 +0000
  Re: list reversal error Mark Lawrence <breamoreboy@yahoo.co.uk> - 2016-03-03 23:20 +0000
  Re: list reversal error Gary Herron <gherron@digipen.edu> - 2016-03-03 15:15 -0800
  Re: list reversal error Steven D'Aprano <steve@pearwood.info> - 2016-03-04 11:06 +1100

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