Leetcode-Medium 2. Add Two Numbers

Example:
Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
Output: 7 -> 0 -> 8
Explanation: 342 + 465 = 807.

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution(object):
    def addTwoNumbers(self, l1, l2):
        if l1 == None:
            return l2
        if l2 == None:
            return l1
        val = l1.val + l2.val
        ansnode=ListNode(val%10)
        ansnode.next=self.addTwoNumbers(l1.next,l2.next)
        if val>=10:
            ansnode.next=self.addTwoNumbers(ListNode(1),ansnode.next)
        return ansnode