leetcode python - addTwoNumbers

# You are given two non-empty linked lists representing two non-negative integers.
# The digits are stored in reverse order and each of their nodes contain a single digit.
# Add the two numbers and return it as a linked list.
#
# You may assume the two numbers do not contain any leading zero, except the number 0 itself.
#
# Input: (2 -> 4 -> 3) + (5 -> 6 -> 4)
# Output: 7 -> 0 -> 8

# Definition for singly-linked list.
class ListNode(object):
def __init__(self, x):
self.val = x
self.next = None

class Solution(object):
def addTwoNumbers(self, l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
def V(val):
return val is not None
result = None
pre = None
tag = 0
while V(l1) or V(l2):
l1_val = V(l1) and l1.val or 0
l2_val = V(l2) and l2.val or 0
val = l1_val + l2_val + tag
tag = val / 10
node = ListNode(val % 10)
if result is None:
result = node
pre = node
else:
pre.next = node
pre = node
if V(l1):
l1 = l1.next
if V(l2):
l2 = l2.next

if tag == 1:
pre.next = ListNode(1)

return result