boundary traversal python

# http://code2begin.blogspot.com
# program to print boundary traversal of a given binary tree


# node class
class node:
    def __init__(self, element):
        self.data = element
        self.left = None
        self.right = None


# function to print the left boundary of the tree
def print_left_boundary(root):
    if root is not None:
        if root.left is not None:
            print(root.data, end=" ")
            print_left_boundary(root.left)
        elif root.right is not None:
            print(root.data, end=" ")
            print_left_boundary(root.right)
    return


# function to print the left boundary of the tree
def print_right_boundary(root):
    if root is not None:
        if root.right is not None:
            print_right_boundary(root.right)
            print(root.data, end=" ")
        elif root.left is not None:
            print_right_boundary(root.left)
            print(root.data, end=" ")
    return


# function to print the leaf nodes of the binary tree
def print_leaves(root):
    if root is not None:
        print_leaves(root.left)
        if root.left is None and root.right is None:
            print(root.data, end=" ")
        print_leaves(root.right)


# function to print the boundary traversal of the binary tree
def boundary_traversal(root):
    print_left_boundary(root)
    print_leaves(root)
    print_right_boundary(root)
    return



head = node(1)
head.left = node(2)
head.right = node(3)
head.left.left = node(4)
head.left.right = node(5)
head.right.right = node(6)
head.left.left.right = node(7)
head.right.right.left = node(8)
head.left.left.right.left = node(9)
head.left.left.right.left.left = node(10)
head.right.right.left.right = node(11)
print("Boundary view of the binary tree is : ")
boundary_traversal(head)