Using recursion to determine the index path of a nested function

Im trying to make a function which finds a value from a list (xs) using another list (index_list) as an index path.

My function should work like this:

xs = [[[1, 2], 3], [4, 5, [6, 7]], 8, [9, 10, 11]]

>>> recursive_index(xs, [1, 2, 0])
6

So far I have:

def recursive_index(xs: List, index_path):

    if not index_path:
        return 0
    
    return recursive_index(xs, index_path[1:]) 

This however just returns 0 for everything, but I don’t know what else the base case should be.

Answer

You’re quite close, but you forgot that at each recursion you actually need to index the list so that you get further in at each recursion. This way, by the time you get to the base case, the variable xs will store the correct result and you can just return it.

This is what the code would look like:

def recursive_index(xs: List, index_path):
    if not index_path:
        return xs
    return recursive_index(xs[index_path[0]], index_path[1:])