implementing Search Tree in Python

Question

I know there are already multiple question on this topics, but none of them has the solution to my problem.

I'm trying to build a Search Tree that has two options:

1. build the tree

2. get from the user a tree and search in it (eg as list, dictionary, ...)

My problem is with the second option, as it appears to be an AttributeError .

When I run my code with no given tree it works fine, but when I try it with a list an error message appears:

    self.root.add(i)
AttributeError: 'NoneType' object has no attribute 'add'

My code:

import unittest
class Testfunction(unittest.TestCase):
  def test(self):
    init = SearchTree(['x', 'b', 'eee'])
    init.add('left')
    init.add('right')
    init.tolist()
    self.assertEqual(init.__contains__('left'),True )
    self.assertEqual(init.add('xx'), None )

class Node:
  def __init__(self, val):
    self.value = val
    self.left = None
    self.right = None
  def insert(self, item):
    if self.value == item:
        return False
    elif self.value > item:
        if self.left:
            return self.left.insert(item)
        else:
            self.right = Node(item)
            return True

  def find(self, item):
    if self.value == item:
        return True
    elif self.value > item:
        if self.left:
           return self.left.find(item)
        else:
           return False
    else:
        if self.right:
            return self.right.find(item)
        else:
            return False

  def tolist(self):
     if self:
         if self.left:
             self.left.tolist()
         if self.right:
             self.right.tolist()

 class SearchTree:
   def __init__(self, items=None):
    # if items . then should be inserted
     self.items = items
     self.root = None
     if items:
         for i in self.items:
             self.root.add(i)


  def __contains__(self, item):
     if self.root:
         return self.root.find(item)
     else:
         return False


  def add(self, item):
    if self.root:
        return self.root.insert(item)
    else:
        self.root  = Node(item)


  def tolist(self):
     self.root.tolist()




test = Testfunction()
test.test()

Answer 1

When you check the items, modify the line to use your built add.

if items:
     for i in self.items:
         # Instead of self.root.add(i)
         self.add(i)