recursion in Python extra brackets

Question

Not sure where i went wrong, but it gives me [-1, [-2, [-3, []]]] instead of just [-1,-2,-3]

def search(list1,list2):
    if list2 == []:
        return list1
    elif list2[0] == list1[0]:
        return [-list1[0] , search(list1[1:],list2[1:])]

print search([1,2,3],[1,2,3])

What are you trying to do ? search for what ? – Nir Alfasi Mar 10 '14 at 03:40 — Nir Alfasi, Mar 10 '14 at 03:40
Code doesn't express your question. – Kei Minagawa Mar 10 '14 at 04:01 — Kei Minagawa, Mar 10 '14 at 04:01

score 2 · Answer 1 · answered Mar 10 '14 at 03:43

I'm not entirely sure what goal your function is aimed at (why return the negative of a matching value?), but you can get your expected output by just concatenating lists in your return statement:

def search(list1,list2):
    if list2 == []:
        return list1
    elif list2[0] == list1[0]:
        return [-list1[0]] + search(list1[1:],list2[1:])

print search([1,2,3],[1,2,3])
# Output:
# [-1, -2, -3]

score 1 · Answer 2 · answered Mar 10 '14 at 03:43

1

If you want to search for elements that are in the same position in both list and make a list with them but changing their sign, you don't need that, you can make it like:

A = [1,2,3]
B = [1,2,3]

print [ -i for i,j in zip(A,B) if i == j]

answered Mar 10 '14 at 03:43

Ruben Bermudez

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recursion in Python extra brackets

2 Answers2