Recursion in Python: Max Depth Exceeded

Question

I am confused how to do recursion in python, when to return and when to update a global variable.

Consider this question: https://leetcode.com/problems/nested-list-weight-sum-ii/

Given a nested list of integers, return the sum of all integers in the list weighted by their depth, where the leaf level integers have weight 1, and the root level integers have the largest weight.

Input: [[1,1],2,[1,1]]

Here is my solution:

class Solution:

    def depthSumInverse(self, nestedList: List[NestedInteger]) -> int:

        md = 0

        def maxdepth(nestedList, m):

            for i in nestedList:

                 if i.isInteger() == False:
                     md = max (m + 1, md)
                     maxdepth(nestedList, m+1)

            return md


        def depthSum(nestedList, maxdepth):

            s = 0

            for i in nestedList:
                t = i.isInteger()
                if t:
                    s += i.getInteger() * maxdepth
                else:
                    s += depthSum(i.getList(), maxdepth-1)

            return s

        m = maxdepth(nestedList, 1)

        return depthSum(nestedList, m)

Recursion Error: Maximum Recursion Depth Exceeded.

How to do recursion while updating md here?

Answer 1

For one thing, I would say that in the last line of this part

    def maxdepth(nestedList, m):

        for i in nestedList:

             if i.isInteger() == False:
                 md = max (m + 1, md)
                 maxdepth(nestedList, m+1)

you probably want to be doing

                 maxdepth(i, m+1)

instead, or you'll just be continually calling maxDepth on the original input list without actually traversing the hierarchy of nested lists.