gistfile1.py

def levelsum(L, k):
    if L.__class__ == int:
        return L

    total = 0
    for element in L:
        total += level_sum(element, k+1)

    if k == 0:
        return total

    return total * (k+1) / float(k)

a = [1, 2, [3, 4, [5]]]
b = [[[[7]]]]
c = []

assert(level_sum(a, 0) == 32)
assert(level_sum(b, 0) == 7*4)
assert(level_sum(c, 0) == 0)