mirror iter bt python

# http://code2begin.blogspot.com
# Program to make a mirror of the binary tree iteratively
# node class
class node:
    def __init__(self, element):
        self.data = element
        self.left = None
        self.right = None


# function to print the preorder traversal of a binary tree
def preorder(root):
    if root is None:
        return

    print(root.data, end=" ")
    preorder(root.left)
    preorder(root.right)


# function to convert tree into mirror tree iteratively
def mirror_tree(root):
    # if the node is null then return
    if root is None:
        return

    # creating a stack to keep the child pointers
    STACK = list()
    # push root node on the stack
    STACK.append(root)

    while len(STACK) > 0:
        # remove the top node from the stack
        current = STACK[0]
        STACK.remove(STACK[0])

        # swap the left and right nodes
        temp = current.left
        current.left = current.right
        current.right = temp

        # as it is a stack, we push right child node first because we want to access it after operating on the left child
        if current.right is not None:
            STACK.append(current.right)

        if current.left is not None:
            STACK.append(current.left)



m1 = node(8)
m1.left = node(3)
m1.right = node(10)
m1.left.left = node(1)
m1.left.right = node(6)
m1.left.right.left = node(4)
m1.left.right.right = node(7)
m1.right.right = node(14)
m1.right.right.left = node(13)

m2 = node(8)
m2.right = node(3)
m2.left = node(10)
m2.left.left = node(14)
m2.right.left = node(6)
m2.right.right = node(1)
m2.left.left.right = node(13)
m2.right.left.left = node(7)
m2.right.left.right = node(4)

print("Tree #1 before mirroring : ")
preorder(m1)
print("\nTree #1 after mirroring : ")
mirror_tree(m1)
preorder(m1)
print("\n\nTree #2 is mirror of Tree #1 to check the correctness : ")
print("TREE #1 : ")
preorder(m1)
print("\nTREE #2 : ")
preorder(m2)