Summing up numbers recursively not working

Asked Nov 18 '14 at 09:19

Active Nov 18 '14 at 10:59

Viewed 45 times

I'm learning about recursion in Python. However, Python is being weird:

def listsum(numslist, _total=0):
if len(numslist) > 1:
    _total += numslist[-1]
    print("Total is %d" % _total)
    numslist = numslist[:-1]
    listsum(numslist, _total)
else:
    _total += numslist[-1]
    print("Returning %d" % _total)
    return _total


if __name__ == '__main__':
    print(listsum([10, 10, 10]))

For me it returns:

Total is 10
Total is 20
Returning 30
None

Can someone tell me what I'm doing wrong?

Edit (fixed)

    listsum(numslist, _total)

Should be

    return listsum(numslist, _total)

edited Nov 18 '14 at 10:59

asked Nov 18 '14 at 09:19

Praetore

2

When `else` is not reached, the function will return `None` by default, that's why you're getting it printed. – Maroun Nov 18 '14 at 09:20
That was stupid. Fixed now! – Praetore Nov 18 '14 at 09:22
This is the single most common mistake with recursive functions I see on SO. – Daniel Roseman Nov 18 '14 at 09:25
1

What is wrong with `sum` and `reduce` ? – Nov 18 '14 at 09:50
The indentation within the function is wrong. It couldn't work that way. Can you please adapt it according to your original code, so that it can't confuse newbies. – cezar Nov 18 '14 at 09:52
I really don't understand what you expect your code to do. – d-coder Nov 18 '14 at 09:57
It's just a code assignment on using recursion in python. I'm familiar with the sum bif, but that wasn't the point. – Praetore Nov 18 '14 at 11:00

Summing up numbers recursively not working

0 Answers0