Newbi Q: Recursively reverse lists but NOT strings?

[Victor B. Gonzalez]

On Sunday 14 October 2007 5:06:19 pm Dmitri O.Kondratiev wrote:
> The function I wrote (below) reverses lists all right:
>
> def reverse(xs):
>     if xs == []:
>         return []
>     else:
>         return (reverse (xs[1:])) + [xs[0]]
>
> >>> reverse ([1,2,3])
>
> [3, 2, 1]
>
> Yet when I try to reverse a string I  get:
> >>> reverse ("abc")
>
> ...
> ...
> ...
>
>   File "C:\wks\python-wks\reverse.py", line 5, in reverse
>
>     return (reverse (xs[1:])) + [xs[0]]
>
>   File "C:\wks\python-wks\reverse.py", line 5, in reverse
>
>     return (reverse (xs[1:])) + [xs[0]]
>
>   File "C:\wks\python-wks\reverse.py", line 2, in reverse
>
>     if xs == []:
>
> RuntimeError: maximum recursion depth exceeded in cmp
>
>
>
> What's wrong? Why recursion never stops?
>
> Thanks,
> Dima


I didn't try anything but it looks like your calling your function in your 
else block like this (e.g., reverse('bc')) everytime. your else block isn't 
really ending itself, just repeating itself.

I could be wrong but from a quick glance you'll need to end it for sure when 
dealing with recursion.

maybe also trying to reverse using the iterator function reversed() or this 
shortcut may help e.g, 'abc'[::-1] -> 'cba'.

good luck!

-- 
Best Regards
Victor B. Gonzalez