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Re: list reversal error

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From MRAB <python@mrabarnett.plus.com>
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Subject Re: list reversal error
Date Thu, 3 Mar 2016 23:20:06 +0000
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On 2016-03-03 23:08, John Gordon wrote:
> 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].
>
A simpler alternative is to use 'reversed':

data1 = list(reversed(data))

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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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