Level-Order Tree Traversal

class Queue(object):

    def __init__(self):
        self.items = []

    def enqueue(self, item):
        self.items.insert(0, item)

    def dequeue(self):
        if not self.is_empty():
            return self.items.pop()

    def is_empty(self):
        return len(self.items) == 0

    def peek(self):
        if not self.is_empty():
            return self.items[-1].value

    def __len__(self):
        return self.size()

    def size(self):
        return len(self.items)


class Node(object):

    def __init__(self, value):
        self.value = value
        self.left = None
        self.right = None

class BinaryTree(object):

    def __init__(self, root):
        self.root = Node(root)

    def print_tree(self, traversal_type):

        if traversal_type == "levelorder":

            return self.levelorder_print(tree.root)

        else:
            print("Traversal type " + str(traversal_type) + " is not supported.")
            return False

    def levelorder_print(self, start):

        if start is None:
            return 

        queue = Queue()


        queue.enqueue(start)

        print('Start Node is:', start.value)

        traversal = ""

        while len(queue) > 0:

            traversal += str(queue.peek()) + "-"

            node = queue.dequeue()

            if node.left:

                queue.enqueue(node.left)

            if node.right:

                queue.enqueue(node.right)

        return traversal


tree = BinaryTree(1)
tree.root.left = Node(2)
tree.root.right = Node(3)
tree.root.left.left = Node(4)
tree.root.left.right = Node(5)

print(tree.print_tree("levelorder"))