CODEWITHSUNDEEP
pythonreturn
user13406539
user13406539

Reputation:

Function returns None no matter what

I have this function which is supposed to give the value of a linked list node by its index. I can print the value the line before but when I return the value it somehow turns into None.

class ListNode:
    def __init__(self, val=0, next_node=None):
        self.val = val
        self.next = next_node


def create_list(linkedlist, i, j=1):
    if i == 0:
        return
    l = ListNode(j)
    linkedlist.next = l
    create_list(linkedlist.next, i-1, j+1)


def index(head, idx=0):
    if idx == 0:
        return head.val
    print(idx)
    index(head.next, idx-1)


link = ListNode()
create_list(link, 5)
print(index(link, 4))

Output:

4
3
2
1
None

I even returned an integer in the function but that turned into None as well.

Any help would be much appreciated.

Upvotes: 0

Views: 85

Answers (1)

thebjorn
thebjorn

Reputation: 27311

You have to return the recursive call as well:

def index(head, idx=0):
    if idx == 0:
        return head.val
    print(idx)
    return index(head.next, idx - 1)

You're missing the return on the last line.

For the other function

def create_list(linkedlist,i,j=1):
    if i == 0:
        return linkedlist   # missing object to return in terminal case
    l = ListNode(j)
    linkedlist.next = l
    return create_list(linkedlist.next,i-1,j+1)  # missing return on recursive call

Upvotes: 1

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