Leetcode: Rotate List @Python

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

class Solution:
    # @param head, a ListNode
    # @param k, an integer
    # @return a ListNode
    def rotateRight(self, head, k):
        if not head: return None
        test=head
        n=1
        while test.next:
            test=test.next
            n+=1
        test.next=head
        for i in range(n-k%n):
            test=test.next
        rst=test.next
        test.next=None
        return rst