01_binary_tree_traversal_preorder.py

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 == "preorder":
            return self.preorder_print(self.root, "")
        else:
            print("Traversal type " + str(traversal_type) + " is not supported.")
            return False

    def preorder_print(self, start, traversal):
        # Root -> Left -> Right

        if start:
            traversal += (str(start.value) + "-")
            traversal = self.preorder_print(start.left, traversal)
            traversal = self.preorder_print(start.right, traversal)

        return traversal


    
'''
    Pre-Order Traversal
    
                    1
                /       \
               2          3
             /   \       /  \  
            4      5    6     7

    1-2-4-5-3-6-7-
'''

        

if __name__ == "__main__":

    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)
    tree.root.right.left = Node(6)
    tree.root.right.right = Node(7)

    X = tree.print_tree("preorder")
    print(X)