Reviewed fork of http://nathanleclaire.com/blog/2014/03/01/build-a-linked-list-for-each-layer-in-a-binary-tree/

treeToLinkedLists.py

class LinkedList:
    next = None
    val = None

    def __init__(self, val):
        self.val = val

    def add(self, val):
        if self.next is None:
            self.next = LinkedList(val)
        else:
            self.next.add(val)

    def __str__(self):
        return "({val}) {next}".format(val=self.val, next=self.next)

class BinaryTree:
    val = None
    left = None
    right = None
	
    def __init__(self, val):
        self.val = val

    def __str__(self):
        return "<Binary Tree (val is {val}). \n\tleft is {left} \n\tright is {right}>".format(val=self.val, left=self.left, right=self.right)

def depth(tree):
    if tree is None:
        return 0
    return 1 + max(depth(tree.left), depth(tree.right))

def tree_to_linked_lists(tree, lists=None, d=None):
    if lists is None:
        lists = {}
    if d is None:
        d = depth(tree)
    if d in lists:
        lists[d].add(tree.val)
    else:
        lists[d] = LinkedList(tree.val)
    if tree.left is not None:
        tree_to_linked_lists(tree.left, lists, d - 1)
    if tree.right is not None:
        tree_to_linked_lists(tree.right, lists, d - 1)
    return lists

if __name__ == '__main__':
	mainTree = BinaryTree(1)
	mainTree.left = BinaryTree(2)
	mainTree.right = BinaryTree(3)
	mainTree.left.left = BinaryTree(4)
	mainTree.left.right = BinaryTree(5)
	mainTree.right.left = BinaryTree(6)
	mainTree.right.right = BinaryTree(7)
	mainTree.right.right.right = BinaryTree(8)
	mainTree.left.left.left = BinaryTree(9)
	ttll = tree_to_linked_lists(mainTree)
	for depthLevel, linkedList in ttll.iteritems():
		print depthLevel, linkedList