recursion gotcha?

[rs387]

On Sep 14, 9:01 am, cnb <circularf... at yahoo.se> wrote:
> def suma(xs, acc=0):
>         if len(xs) == 0:
>                 acc
>         else:
>                 suma(xs[1:], acc+xs[0])
>
> it returns none.

Yep, that's because there is no "return" statement anywhere. Python
doesn't return expressions "by default", like functional languages do,
so where you say "suma(xs[1:], acc+xs[0])" this just calls itself and
returns nothing.

Try this:

def suma(xs, acc=0):
        if len(xs) == 0:
                return acc
        else:
                return suma(xs[1:], acc+xs[0])

print suma([1, 2, 3, 4, 5])

(prints 15)

Roman