Binary tree in-order python

Question

I'm creating a binary tree and I'm stuck to convert it to postfix and infix. The problem is that I'm trying to create a method infix and postfix inside the class but it doesn’t work:

TypeError: Node.Postfix() takes 1 positional argument but 2 were given

class Node:
    def __init__(self, key):
        self.left = None
        self.right = None
        self.val = key

    def Postfix(self):
            if Node:
              self.Postfix(self.left)
              self.Postfix(self.right)
              print(Node.val, end=" ")

X="- + a b * * e f g"

r=Node.constructTree(X)

r.Postfix()

I'm building my tree using the stack.

Answer 1

The main problem is that you use Postfix method with an argument, but it doesn't accept one.

In Python the methods are like functions, but their first argument (self) is an object. So, to call the Postfix method on the left subtree use should use self.left.Postfix().

Another problem is that before calling Postfix you should test if the subtree exists. And you should use self.val instead of Node.val to get a value of the node.

If you fix all these errors you get something like this:

def Postfix(self):
    if self.left:
        self.left.Postfix()
    if self.right:
        self.right.Postfix()
    print(self.val, end=" ")