Linked List class based implementation in Python
First, there are some awkwardnesses in your code:


You should not use next as a variable because, it is a built-in function.
The getContents function is useless, because contents is a public attribute.
Your print_list method is ill-formed, you need to use self.


You can simplify like this:

class Node:
    def __init__(self,contents=None, next_node=None):
        self.contents = contents
        self.next_node = next_node

    def __str__(self):
        return str(self.contents)

    def print_list(self):
        node = self
        while node is not None:
            print(node.contents)
            node = node.next_node
        print()


To test your code, you can use the Unit Testing Framework, for instance:

import unittest

class TestNode(unittest.TestCase):

    def test_construcor(self):
        node1 = Node("A")
        node2 = Node("C")
        node3 = Node("D")
        node4 = Node("B")
        # Define the pointers for each node (e.g. follow through A to B to C to D)
        node1.next_node = node4
        node4.next_node = node2
        node2.next_node = node3
        node1.print_list()
        self.assertEqual(node1.next_node.contents, 'B')

if __name__ == '__main__':
    unittest.main()