test.py

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

class Solution(object):
	def reverseList(self, head):
		prev = None

		while head:
			next = head.next
			head.next = prev
			prev = head
			head = next

		return prev