leetcode-Merge Two Sorted Lists

class Solution:
# @param {ListNode} l1
# @param {ListNode} l2
# @return {ListNode}
def mergeTwoLists(self, l1, l2):
if l1 is None: return l2
if l2 is None: return l1

if l1.val > l2.val:
l1, l2 = l2, l1
l1.next = self.mergeTwoLists(l1.next, l2)
return l1