Python: Unexpected result in a recursive function

Question

I've written a recursive function to gauge, e.g. list depth and for some reason it returns unexpected results.

I have two functions: 1. checks if the object is iterable 2. gauges the depth of the object, e.g. list

I think I'm missing something in the second function but I couldn't wrap my head around why exactly variable n when returned from else turns into a funny result. I set print to see how n gets changed in every stage and it seemed working as expected but when returned from else it turns into a wrong number.

Here are two functions' code:

def isiterable(obj):
    '''
    takes in an obj and returns 1 if iterable or 0 if not
    strings are discarded as iterable
    :param obj: any object
    :return: int
    '''
    if isinstance(obj, str):
        return 0
    else:
        try:
            iter(obj)
            return 1
        except TypeError as err:
            return 0

my second function is recursive where I'm experiencing problems

def get_depth(a, n=0):

    if isiterable(a):
        return n + f(a[0], n+1)

    else:
        return n

I've three examples:

a = [[[1,2], [3,4]], [[5,6],[7,8]]]
b = [[1,2], [2,3]]
c = [2]

I'm expecting get_depth to return 3 for list a, 2 for list b and 1 for list c.

for some reason results for a get doubled and return 6. In b case it is 3 instead of 2.

Many thanks

Daeho Ro · Accepted Answer · 2019-09-29 00:15:27Z

1

You don't need to add n when you return from get_depth.

def get_depth(a, n=0):

    if isiterable(a):
        return get_depth(a[0], n+1)

    else:
        return n

Because, when a have more depth, you will calculate the get_depth function again witn n+1 which is already count the depth correctly and the extras are not needed.

Btw, you have to think about what if this case?

d = [1, 2, [3, 4]]

I can modify a bit such as:

def get_depth(a, n=0):

    if isiterable(a):
        temp = []
        for i in range(0, len(a)):
            temp.append(get_depth(a[i], n+1))

        return max(temp)

    else:
        return n

answered Sep 29, 2019 at 0:15

Daeho Ro

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