I'm creating a basic binary search tree program where the nodes have to be strings however, I keep getting this error:
'builtins.AttributeError: 'NoneType' object has no attribute 'addNode'
I'm a bit confused because I thought you had to declare the children nodes as None. My code is below (please excuse the messiness and extra print statements):
class BinarySearchTree:
#constructor with insertion value & left/right nodes as None
def __init__(self, data):
self.data = data
self.left = None
self.right = None
#function to insert node
def addNode(root, data):
#when tree doesn't exist
if root == None:
return BinarySearchTree(data)
else:
#when node is already in tree
if root.data == data:
return root
#smaller values go left
elif data < root.data:
root.left.addNode(data)
#bigger values go right
else:
root.right.addNode(data)
return root
#function to find smallest node value (to help with deletion)
def smallestNode(root):
node = root
#loop goes to lowest left leaf
while(node.left is not None):
node = node.left
return node
#function to delete node
def removeNode(root, data):
if root == None:
return root
#when node to be deleted in smaller than root, go left
if data < root.data:
root.left = root.left.removeNode(data)
#when node to be deleted in bigger than root, go right
elif data > root.data:
root.right = root.right.removeNode(data)
##when node to be deleted in the same as root...
else:
#when node has only 1 or 0 children
if root.right == None:
move = root.left
root = None
return move
elif root.left == None:
move = root.right
root = None
return move
#when node has 2 children, copy then delete smallest node
move = root.right.smallestNode()
root.data = move.data
root.right = root.right.removeNode(move.data)
return root
def findNode(root, data):
#if current node is equal to data value then return the root
if root.data == data or root == None:
return root
#if current node is greater than the data value then, search to the left
elif data < root.data:
return root.left.findNode(data)
#if current node is less than the data value then, search to the right
else:
return root.right.findNode(data)
def createBST(keys):
root = BinarySearchTree(keys[0])
for i in range(1,len(keys)):
root.addNode(keys[i])
return root
print('Hi! Welcome to the Binary Search Tree Builder')
print('Here are your options below:')
print('1) Build new tree')
print('2) Add a node')
print('3) Find a node')
print('4) Delete a node')
choice = int(input('What would you like to do?: '))
if choice == 1:
nodes = list(input("Enter the strings you would like to build your tree from (separate by a space): ").split())
print(nodes)
tree = createBST(nodes)
print(tree)
I'm wondering where exactly is this error coming from and how can I fix it? Also, if you see any other problems occuring in my code, please let me know!
You have conflated the notion of "tree node" and "tree". What you have there is a mixture of the two. Remember, the first parameter to ALL member functions should be "self". Replacing "root" by "self" might make your problem more clear.
So, you might create a BinaryTree class, which has a single member called self.root that holds a BinaryTreeNode object, once you have a node. The nodes will hold the left and right values, each of which will either have None or a BinaryTreeNode object. The node class probably doesn't need much code -- just self.left and self.right.
The BinaryTree class will have an addNode member that knows how to traverse the tree to find the right spot, but when you find the spot, you just set self.left = BinaryTreeNode(...). A node does not know about the tree, so a node does not know how to add new nodes. That's a function of the tree itself.
Does that make your path forward more clear?