How can I count the depth in a list of lists?

I want to count the depth in a list of lists, so not the amount of elements but the maximum depth one list can have.

This is my function:

def max_level(lst):

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

should return 4

Answer

You can try:

def max_level(lst):
    return isinstance(lst, list) and max(map(max_level, lst)) + 1

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

Output:

4

Explanation:

1. First check if object passed into the recursive function is of type list:

def max_level(lst):
    return isinstance(lst, list)

2. If so, proceed to add up the Trues in the list:

and max(map(max_level, lst)) + 1

where the max(map(max_level, lst)) returns the current amount of Trues, and the + 1 is to add one more.

---

If there can be empty lists, you can replace lst with lst or [0], where the or will tell python to use the list on the left side of it if its not empty, else use the [0]:

def max_level(lst):
    return isinstance(lst, list) and max(map(max_level, lst or [0])) + 1

print(max_level([1, [], [[]]]))

Output:

3

---

Addressing @cdlane’s comment, if you don’t want to mix boolean values with integer values, you can add an int() wrapper to the isinstance() call:

def max_level(lst):
    return int(isinstance(lst, list)) and max(map(max_level, lst or [0])) + 1