Tree insertion and variable referencing

[hshivaraj]

Hey all!
This is probably very basic for some people , but i really cant get my head around this.

The code below performs binary tree insertion. The thing i cant understand is, you'll notice in the _insert function return root. I really dont see the point of that return. However with out that return root. The tree doesn't parse. But however in the calling function insert i dont assign that returned value from _insert to anything. Yet its required. Please help me understand this?

    def insert(self, val):
        if self.root is None:
            self.root = Node(val)
        else:
            self._insert(self.root, val)

    def _insert(self, root, val):
        print(id(root))
        if root is None:
            return Node(val)
        if val <= root.val:
            root.left = self._insert(root.left, val)
        else:
            root.right = self._insert(root.right, val)
        return root

[Windspar]

because it recursive function. root.left and root.right need a node.

root.left = self._insert(root.left, val) # need the return

---

I believe it to be. None is not a reference variable.

---

you could also do this.

class Root:
	def __init__(self):
		self.root = None
		
	def insert(self, val, root='self'):
		if root == 'self':
			self.root = self.insert(val, self.root)			
		elif root is None:
			return Node(val)
		elif val <= root.value:
			root.left = self.insert(val, root.left)
		else:
			root.right = self.insert(val, root.right)
		return root

[hshivaraj]

def insert(self, val, root='self'):[b][/b]

Clever - I didn't know you can do that. Assign self as default argument as a string.

[Windspar]

'self' is just a string. This just check it.

def insert(self, val, root='self'):
        if root == 'self':
            self.root = self.insert(val, self.root)

As long as root is not None or a Node. You can have it be anything else.

def insert(self, val, root=True):
        if root is True:
            self.root = self.insert(val, self.root)