class Node(object):
    """ Class in a linked list. """

    def __init__(self, data, next=None):
        self.data = data
        self.next = next

    def as_string(self):
        """Represent data for this node and it's successors as a string.

        >>> Node(3).as_string()
        '3'

        >>> Node(3, Node(2, Node(1))).as_string()
        '321'
        """

        out = []
        n = self

        while n:
            out.append(str(n.data))
            n = n.next

        return ''.join(out)


def reverse_linked_list(head):
    """Given singly linked list head node, return head node of new, reversed linked list.

    >>> ll = Node(1, Node(2, Node(3)))
    >>> reverse_linked_list(ll).as_string()
    '321'

    >>> ll = Node(1, Node(2, Node(3)))
    >>> new_ll = reverse_linked_list(ll)
    >>> new_ll.as_string()
    '321'
    """

    prev = None
    curr = head

    while curr:
        next = curr.next
        curr.next = prev
        prev = curr
        curr = next


    return prev











if __name__ == '__main__':
    import doctest
    results = doctest.testmod()

    if results.failed == 0:
        print "ALL TESTS PASSED!"