python finding depth of a list using recursion

Question

I need to find the depth of a list using recursion but and I can't use global variables or have more than one parameter. this is the code that I have but I'm getting the error where I can't call depth because I cant use a global variable and when I call it inside the function when the recursion happens it just resets the variable

def how_deep(list_of_lists):
    for i in list_of_lists:
        if type(i) == list:
            how_deep(i)
            depth += 1
        else:
            print(depth)


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

i have to keep the if name equals main portion the same or else i would just add another parameter — Jerry Thomas
– Jerry Thomas, Commented Dec 2, 2021 at 5:31

flakes · Accepted Answer · 2021-12-02 05:37:28Z

4

As you loop through each item you want to record its maximum depth and return the maximum depth of an individual child in the list. You could do something like this:

def how_deep(list_of_lists):
    if not isinstance(list_of_lists, list):
        return 0
    return max(map(how_deep, list_of_lists), default=0) + 1

answered Dec 2, 2021 at 5:37

flakes

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4 Comments

Jerry Thomas Over a year ago

yeah i would use that but i cant use the isinstance keyword either this class is killing me

flakes Over a year ago

@JerryThomas then just change not isinstance(list_of_lists, list) to type(list_of_lists) != list

flakes Over a year ago

@JerryThomas Or if you know the elements will always be lists, then you can remove that if check altogether.

flakes Over a year ago

@JerryThomas you could also wrap it in try: ... except TypeError: return 0 to avoid the check. That would actually be slightly faster in the nominal case where everything is a list.

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