python leetcode 148. Sort List

class Solution(object):
    def sortList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        
        res=[]
        while head:
            res.append(head.val)
            head=head.next 
        res.sort()
        p=ListNode(0)
        s=p
        for r in res:
            p.next=ListNode(r)
            p=p.next
        return s.next