Nested List Weight Sum

Given a nested list of integers, return the sum of all integers in the list weighted by their depth.

Each element is either an integer, or a list -- whose elements may also be integers or other lists.

Example 1: Given the list [[1,1],2,[1,1]], return 10. (four 1's at depth 2, one 2 at depth 1)

Example 2: Given the list [1,[4,[6]]], return 27. (one 1 at depth 1, one 4 at depth 2, and one 6 at depth 3; 1 + 42 + 63 = 27)

URL: https://leetcode.com/problems/nested-list-weight-sum/

# """
# This is the interface that allows for creating nested lists.
# You should not implement it, or speculate about its implementation
# """
#class NestedInteger(object):
#    def isInteger(self):
#        """
#        @return True if this NestedInteger holds a single integer, rather than a nested list.
#        :rtype bool
#        """
#
#    def getInteger(self):
#        """
#        @return the single integer that this NestedInteger holds, if it holds a single integer
#        Return None if this NestedInteger holds a nested list
#        :rtype int
#        """
#
#    def getList(self):
#        """
#        @return the nested list that this NestedInteger holds, if it holds a nested list
#        Return None if this NestedInteger holds a single integer
#        :rtype List[NestedInteger]
#        """

class Solution(object):
    def depthSum(self, nestedList):
        """
        :type nestedList: List[NestedInteger]
        :rtype: int
        """
        return self.depthSum_helper(nestedList, 1)

    def depthSum_helper(self, nested_list, depth):
        if len(nested_list) == 0 or nested_list == None:
            return 0
        else:
            sum = 0
            for entries in nested_list:
                if entries.isInteger():
                    sum += entries.getInteger()*depth
                else:
                    sum += self.depthSum_helper(entries.getList(), depth + 1)

            return sum