Binary search tree implementation in Python

Question

I am reading about algorithms and got to the binary search trees. I wanted to ask if the following implementation of a Binary Tree is correct.

import random
class Tree(object):
 def __init__(self):
 self.root = Node()
 def insert(self,data):
 self.root.insert(data)
 def delete(self,data):
 self.root.delete(data)
 def print_elements(self):
 return self.root.print_element()
class Node(object):
 def __init__(self,data = None, parent = None):
 self.parent = parent
 self.data = data
 self.left = None
 self.right = None
 def insert(self,data):
 if self.data == None:
 self.data = data
 else:
 if data < self.data:
 if self.left == None:
 self.left = Node(data,self)
 else:
 self.left.insert(data)
 else:
 if data > self.data:
 if self.right == None:
 self.right = Node(data,self)
 else:
 self.right.insert(data)
 def delete(self,data):
 if self.data == data:
 if self.right == None and self.left == None: 
 if self.parent.left.data == data:
 self.parent.left = None
 else:
 self.parent.right = None
 elif self.right == None or self.left == None:
 if self.right == None:
 self.data , self.left = self.left.data , self.left.left
 else:
 self.data, self.right = self.right.data , self.right.right
 else:
 counter = self.right
 while True:
 if counter.right == None:
 break
 else:
 counter = counter.left
 self.data = counter.data
 counter.delete(counter.data)
 else:
 if data < self.data:
 self.left.delete(data)
 else:
 self.right.delete(data)
 def search(self,data):
 if self.data == data:
 return self.data
 else:
 if data < self.data:
 return self.left.search(data)
 else:
 return self.right.search(data)
 def print_element(self):
 if self.parent:
 print self.data, 'is below %s' % (self.parent.data)
 else:
 print self.data
 if self.right != None:
 self.right.print_element()
 if self.left != None:
 self.left.print_element()

The other thing I want to ask is, when I am implementing these data structures (also happened with linked lists) I find it easier to implement the methods in the Node class and not in the BT/LL class. Is this normal with Python ? I mean, I see the guides with C++ and the methods are mostly implemented in the BT/LL classes , but they use pointers and pointers are not available in Python. Am I doing it wrong ?

• 301_Moved_Permanently: Is it on purpose that your implementation can not hold more than one identical value? I mean, t = Tree(); t.insert(1); t.insert(1) result in t containing only one node. Why?
• Martin Spasov: Yep, I am not sure how I should handle the same value more than once and this is why I did not include it in the implementation
• greybeard: (I wanted to ask ... not holding my breath 'til you do...) Tag python-2x.

Answer 1

[is below] implementation of a Binary Tree [correct?]
Without a specification of how a Binary (Search) Tree is to behave, that is difficult to tell, Asian style.
Try

if __name__ == '__main__':
 t = Tree()
 t.insert(0)
 t.delete(1)
 t.delete(0)

: While it may be possible to hand-wave failure to delete something not in the tree,
not being able to delete what's in a single-item tree is not correct.