Implementing Binary search tree in python?

Question

I am trying to do insert function in python for BST but I am just confused on how to access the public methods properly and its giving me some grief, right now when I test it it just stops at the first test and says nonetype object has no attribute data but how am I suppose to access data when t = tree() and tree doesn't have a data constructor?

class Node(object):
    def __init__(self, data):
       self.parent = None
       self.left = None
       self.right = None
       self.data = data

class Tree(object):
# Binary Search Tree
# class constants
PREORDER = 1
INORDER = 2
POSTORDER = 3

   def __init__(self):
    # Do not create any other private variables.
    # You may create more helper methods as needed.
       self.root = None

   def print(self):
    # Print the data of all nodes in order
      self.__print(self.root)


   def __print(self, curr_node):
    # Recursively print a subtree (in order), rooted at curr_node
       if curr_node is not None:
           self.__print(curr_node.left)
           print(str(curr_node.data), end=' ')  # save space
           self.__print(curr_node.right)


   def insert(self, data):
    # Find the right spot in the tree for the new node
    # Make sure to check if anything is in the tree
    # Hint: if a node n is null, calling n.getData() will cause an error
      root = Node(data)
      print("this is my", self.root)
      if self.root is None:
          self.root = root
          return Node(data)
      else:
          if root.data == data:
              return root
          elif root.data < data:
              root.right = insert(root.right,data)
          else:
              root.left = insert(root.left, data)
      return root

And this is the test cases that I'm running with

import lab3
import unittest

class T0_tree__insert(unittest.TestCase):

    def test_balanced_binary_search_tree(self):
        print("\n")
        print("tree_insert_with_individual_check")
        t = lab3.Tree()

        t.insert(4)
        t.insert(2)
        t.insert(6)
        t.insert(1)
        t.insert(3)
        t.insert(5)
        t.insert(7)

        #The following check is without using tree as an iterator (which uses inorder traversal)
        #So this function also does not check the implementation of the traversal function

        self.assertEqual(t.root.data, 4)
        self.assertEqual(t.root.left.data, 2)
        self.assertEqual(t.root.left.left.data, 1)
        self.assertEqual(t.root.left.right.data, 3)
        self.assertEqual(t.root.right.data, 6)
        self.assertEqual(t.root.right.left.data, 5)
        self.assertEqual(t.root.right.right.data, 7)

        print("\n")

Answer 1

Provided two options

1. Adds a helper function for insert to Tree (similar to helper print function __print). This allows keeping track of node we are traversing in the tree
2. Non-recursive insert which processes through nodes.

Both options satisfy unittest.

Option 1 - Add a utility function to insert

File labe3.py

class Node(object):
    def __init__(self, data):
        self.parent = None
        self.left = None
        self.right = None
        self.data = data

class Tree(object):
    # Binary Search Tree
    # class constants
    PREORDER = 1
    INORDER = 2
    POSTORDER = 3

    def __init__(self):
        # Do not create any other private variables.
        # You may create more helper methods as needed.
        self.root = None

    def print(self):
        # Print the data of all nodes in order
        self.__print(self.root)

    def __print(self, curr_node):
        # Recursively print a subtree (in order), rooted at curr_node
        if curr_node is not None:
            self.__print(curr_node.left)
            print(str(curr_node.data), end=' ')  # save space
            self.__print(curr_node.right)

    def insert(self, d):
        print("this is my", self.root)
        if self.root is None:
          self.root = Node(d)
        else:
          self._insert(self.root, d) # here's the call to a "private" function to which we are passing nodes down, starting from root

    def _insert(self, node, value):
        ''' helper function for insert 
               node - node in BST to add value
               value - value to add
        '''
        if value < node.data:  # we know that `node` cannot be None 
                               # so it's safe to check its value! 
              if node.left:
                self._insert(node.left, value) # the recursive call is done only when `node.left` is not None
              else:
                node.left = Node(value)  # direct assignment
        else:
            if node.right:
                self._insert(node.right, value)
            else:
                node.right = Node(value)  # direct assignment
        

Option 2-non-recursive insert function

File labe3.py

class Node(object):
    def __init__(self, data):
        self.parent = None
        self.left = None
        self.right = None
        self.data = data

class Tree(object):
    # Binary Search Tree
    # class constants
    PREORDER = 1
    INORDER = 2
    POSTORDER = 3

    def __init__(self):
        # Do not create any other private variables.
        # You may create more helper methods as needed.
        self.root = None

    def print(self):
        # Print the data of all nodes in order
        self.__print(self.root)

    def __print(self, curr_node):
        # Recursively print a subtree (in order), rooted at curr_node
        if curr_node is not None:
            self.__print(curr_node.left)
            print(str(curr_node.data), end=' ')  # save space
            self.__print(curr_node.right)

    def insert(self, d):
        print("this is my", self.root)
        if self.root is None:
          self.root = Node(d)
        else:
          # current node
          current = self.root

          # Finds node to add data
          while True:
              if current.data > d:
                  if current.left == None:
                      current.left = Node(d)
                      break
                  else:
                      current = current.left

              elif current.data < d:
                  if current.right == None:
                      current.right = Node(d)
                      break
                  else:
                      current = current.right

              else:  
                break
       

File main.py

import lab3
import unittest

class T0_tree__insert(unittest.TestCase):

    def test_balanced_binary_search_tree(self):
        print("\n")
        print("tree_insert_with_individual_check")
        t = lab3.Tree()

        t.insert(4)
        t.insert(2)
        t.insert(6)
        t.insert(1)
        t.insert(3)
        t.insert(5)
        t.insert(7)

        #The following check is without using tree as an iterator (which uses inorder traversal)
        #So this function also does not check the implementation of the traversal function

        self.assertEqual(t.root.data, 4)
        self.assertEqual(t.root.left.data, 2)
        self.assertEqual(t.root.left.left.data, 1)
        self.assertEqual(t.root.left.right.data, 3)
        self.assertEqual(t.root.right.data, 6)
        self.assertEqual(t.root.right.left.data, 5)
        self.assertEqual(t.root.right.right.data, 7)

        print("\n")
        
if __name__ == '__main__':
    unittest.main()

Output

tree_insert_with_individual_check
this is my None
this is my <lab3.Node object at 0x7fa4386b92e0>
this is my <lab3.Node object at 0x7fa4386b92e0>
this is my <lab3.Node object at 0x7fa4386b92e0>
this is my <lab3.Node object at 0x7fa4386b92e0>
this is my <lab3.Node object at 0x7fa4386b92e0>
this is my <lab3.Node object at 0x7fa4386b92e0>


.
----------------------------------------------------------------------
Ran 1 test in 0.001s

OK