assigning name to tree node using classes in Python

Question

how do I assign a name to the left child of the left child of the root? I am new with classes. the last two lines are where I try to make the assignment. Help is appreciated!

class BinaryTree:
 def __init__(self,rootName):
 self.root = rootName
 self.leftChild = None
 self.rightChild = None
 def insertLeft(self,newNode):
 if self.leftChild == None:
 self.leftChild = BinaryTree(newNode)
 else:
 t = BinaryTree(newNode)
 t.leftChild = self.leftChild
 self.leftChild = t
 def insertRight(self,newNode):
 if self.rightChild == None:
 self.rightChild = BinaryTree(newNode)
 else:
 t = BinaryTree(newNode)
 t.rightChild = self.rightChild
 self.rightChild = t
 def getRightChild(self):
 return self.rightChild
 def getLeftChild(self):
 return self.leftChild
 def setRootVal(self,obj):
 self.root = obj
 def getRootVal(self):
 return self.root
r = BinaryTree('a')
r.leftChild = 'b'
r.rightChild = 'c'
r.insertLeft = BinaryTree('b')
r.insertRight = BinaryTree('c')
r.getLeftChild().leftChild = 'd' 
r.leftChild.leftChild = 'd'

both of the last two statements give me this error: 'str' object has no attribute 'getRootVal' I am trying to create a tree that looks like this: enter image description here

• Sweeper: You don't seem to understand how to use the BinaryTree class. What does the homework require you to do?
• Rahel Miz: hi, trying to create a tree that looks like this above
• Rohan Kaushik: insertLeft and insertRight are functions, not attributes. As such you should be doing r.insertLeft('b') and r.insertRight('c'). The code runs after this modification, although I agree with @Sweeper and you could implement this better.
• Rahel Miz: thank you! first time doing OOP. What would be the better implementation?

Answer 1

Looking at the interface of BinaryTree, you are supposed to call insertLeft and insertRight to add children to the tree, instead of:

r.leftChild = 'b'
r.rightChild = 'c'

leftChild and rightChild are supposed to be BinaryTree objects, not strings. Although you could write:

r.leftChild = BinaryTree('b')
r.rightChild = BinaryTree('c')

It doesn't handle the case when leftChild and rightChild are not None. This is why you should use insertLeft and insertRight, which does handle these cases for you:

r.insertLeft('b')
r.insertRight('c')

To insert d, e and f, we do it the same way using insertLeft and insertRight:

r.getLeftChild().insertRight('d')
r.getRightChild().insertLeft('e')
r.getRightChild().insertRight('f')