NameError When Implementing Inorder Traversal

Question

I'm trying to implement a Binary Search Tree in Python, and I'm having difficulty in understanding the NameError I get when I call the inorder traveral method on my tree. I have already created a BST instance, and I've defined the in_order_traversal() method before I call it on the instance, so why am I getting a NameError?

class BSTNode:

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

class BST:

def __init__(self):
    self.root = None

def insert(self,data):
    new_node = BSTNode(data)

    if self.root == None:
        self.root = new_node
    else:
        ptr = self.root
        prev = None

        while ptr != None:
            prev = ptr
            if data <= ptr.data:
                ptr = ptr.left
            else:
                ptr = ptr.right
        if data <= prev.data:
            prev.left = new_node
        else:
            prev.right = new_node

def in_order_traversal(self):
    if self.root != None:
        in_order_traversal(self.root.left)
        print(root.data)
        in_order_traversal(self.root.right)


bst = BST()
bst.insert(50)
bst.insert(25)
bst.insert(100)
bst.insert(80)
bst.insert(30)
bst.in_order_traversal()

Answer 1

You forgot the self.

def in_order_traversal(self):
    if self.root != None:
        self.in_order_traversal(self.root.left)
        print(root.data)
        self.in_order_traversal(self.root.right)