Program for n’th node from the end of a Linked List

Given a Linked List and a number n, write a function that returns the value at the n’th node from end of the Linked List.

class SingleLinkedList(object):
    def __init__(self,val):
        self.value = val
        self.next = None

    def __repr__(self):
        return str(self.value)

class Solution(object):
    def find_nth_node_from_last(self, head,n):
        slow_ptr = head
        fast_ptr = head

        for _ in range(n):
            if not fast_ptr:
                return None
            fast_ptr = fast_ptr.next
        print fast_ptr    
        while fast_ptr:
            fast_ptr = fast_ptr.next
            slow_ptr = slow_ptr.next

        return slow_ptr