太傻了 。。总之上代码：
# Definition for singly-linked list.
# class ListNode(object):
# def __init__(self, x):
# self.val = x
# self.next = None
class Solution(object):
def mergeTwoLists(self, l1, l2):
"""
:type l1: ListNode
:type l2: ListNode
:rtype: ListNode
"""
if l1 == None:
return l2
elif l2 == None:
return l1
dump = ListNode(0)
head = dump
while l1 and l2:
if l1.val < l2.val:
head.next = ListNode(l1.val)
head = head.next
l1 = l1.next
else:
head.next = ListNode(l2.val)
head = head.next
l2 = l2.next
if l1 :
head.next = l1
elif l2:
head.next = l2
else:
head.next = None
return dump.next
