Search Binary Tree in Python (In-order traversal error)

Question

I have a theoretical question and as well small mistake, so I am calling inorder_traversal function which was supposed to order the binary tree an it gives me an error inorder_traversal() takes 0 positional arguments but 1 was given. I gave zero arguments and I called zero arguments. So that is the first question and the second one ism so this inorder_traversal function, how does it go from the furthest left up. I didn't quite catch that last part?

class BinarySearchTree:
 def __init__(self, value):
 self.left = None
 self.right = None
 self.value = value
 
 def insert(self, value):
 #checking if value that we are trying to insert is less then the current value
 if value < self.value:
 if self.left is None:
 #if the left node is not existing then we are going to create it
 self.left = BinarySearchTree(value)
 else:
 self.left.insert(value)
 else:
 if self.right is None:
 self.right = BinarySearchTree(value)
 else:
 self.right.insert(value)
 def inorder_traversal():
 if self.left:
 self.left.inorder_traversal()
 print(self.value)
 if self.right:
 self.right.inorder_traversal()
 
 
tree = BinarySearchTree(15)
tree.insert(14)
tree.insert(20)
tree.insert(7)
tree.insert(8)
tree.insert(1)
tree.insert(70)
tree.inorder_traversal()

• Mike Scotty: inorder_traversal should probably be an instance method. As such you need to write def inorder_traversal(self): (notice the self argument).

Answer 1

For the first question the answer is that if you called an instance method in python then a self object is passed as an argument to the function so you need to include that parameter in your class function:

def inorder_traversal(self):

This line:

tree.inorder_traversal()

Is equivalent to:

BinarySearchTree.inorder_traversal(tree)

And for the second question you can see this video on youtube it explains the different traversal ordering of binary trees: https://www.youtube.com/watch?v=-b2lciNd2L4