Python list function

list.py

class Solution(object):
	def addTwoNumbers(self, l1, l2):
		ll1 = self.list2naive(l1)
		ll2 = self.list2naive(l2)
		a = 0 if ll1 == [] else int(''.join(map(str, ll1))[::-1])
		b = 0 if ll2 == [] else int(''.join(map(str, ll2))[::-1])
		res = a + b
		return self.naive2list(map(int, list(str(res)[::-1])))

	def list2naive(self, l):
		ret = []
		while l:
			ret.append(l.val)
			l = l.next
		return ret

	def naive2list(self, xs):
		if not xs:
			None
		else:
			h = xs.pop(0)
			tail = self.naive2list(xs)
			hh = ListNode(h)
			hh.next = tail
			return hh

	def test(self):
		xs = self.naive2list([1,2,3])
		ys = self.naive2list([2,3,4,5])
		zs = self.naive2list([])
		p1 = self.naive2list([5])
		rs = self.list2naive(self.addTwoNumbers(xs, ys))
		rs2 = self.list2naive(self.addTwoNumbers(xs, zs))
		print rs
		assert(rs == [3,5,7,5])
		assert(rs2 == [1,2,3])
		assert(self.list2naive(self.addTwoNumbers(p1, p1)) == [0, 1])
		return 'test pass'