list reversal error
Gary Herron
gherron at digipen.edu
Thu Mar 3 18:15:19 EST 2016
On 03/03/2016 02:51 PM, vlyamtsev at gmail.com wrote:
> 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
Look at the values (say with a print) you get from your line
j = len(data) - i
You'll find that that produces (with a list of 4 elements for example)
4,3,2,1 when in fact you want 3,2,1,0. Soo you really want
j = len(data) - i -1
Better yet, use more of Python with
data1 = list(reversed(data))
Or don't even make a new list, just reverse the original list in place
>>> L=[1,2,3]
>>> L.reverse()
>>> L
[3, 2, 1]
Or even better, if you simply want to iterate through the original list,
but in reverse order:
for datum in reversed(data):
... whatever with datum ...
which wastes no time actually reversing the list, but simply loops
through them back to front.
Gary Herron
--
Dr. Gary Herron
Department of Computer Science
DigiPen Institute of Technology
(425) 895-4418
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