How can I run this Height of a BST tree function

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can someone help me out with this? I implemented a binary search tree data structure in python and I wrote a BST_height() function to calculate the height of the tree. But when I ran my code, It gave me an error saying 'self is not defined'. I know why the error is showing up but can you suggest some other way to run the BST_height function with the root node 

class Node:

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

class BinarySearchTree:

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

    def display(self):

        print('''
                {}
              /   \\
             {}    {}
            / \\   / \\
          {}   {} {} {}  

           BINARY TREE         
        '''.format(tree.root.data, tree.root.left.data, tree.root.right.data, tree.root.left.left.data, tree.root.right.right.data, tree.root.left.right.data, tree.root.right.left.data))

    def checkRoot(self):

        if self.root.data != None:
            return 'Root node exists'
        else:
            return 'Root node doesn\'t exists'    

    def insert(self, data):
        newNode = Node(data)

        if self.root.data == None:
            # creating the root node 
            self.root = newNode
        else:
            self.insertNode(data, self.root)

    def insertNode(self, data, curNode):

        if data < curNode.data:
            if curNode.left == None:
                curNode.left = Node(data)
            else:
                self.insertNode(data, curNode.left)

        elif data > curNode.data:
            if curNode.right == None:
                curNode.right = Node(data)
            else:
                self.insertNode(data, curNode.right)

        else:
            print('The value already exists ha ha')# funny 

    def BST_height(self, node):                     

        if node == None:
            return -1

        leftHeight = height(node.left)
        rightHeight = height(node.right)

        return max(leftHeight, rightHeight) + 1 



tree = BinarySearchTree()
tree.insert(30)# root node 
tree.insert(24)
tree.insert(45)
tree.insert(90)
tree.insert(18)
tree.insert(28)
tree.insert(40)
tree.display()

# getting an error here
# I know self.root can\'t be used outside the class but can you suggest some other way tree.BST_height(self.root)
height data-structures python
1 Answers

There are 2 problems with the code:

  1. Self is something you use inside of class functions. Outside you can simply use the object variable. like so:
tree.BST_height(tree.root)
  1. BST_height function has a small error in it. It calls height instead of self.BST_height:
def BST_height(self, node):
    if node == None:
        return -1

    leftHeight = self.BST_height(node.left)
    rightHeight = self.BST_height(node.right)

    return max(leftHeight, rightHeight) + 1

You might want to read this for clarity on the whole self topic.

user_7888330
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