Traversing a Binary Search Tree Python

Question

I'm struggling to get the hang of traversing a binary search tree I think I have my code right but I keep getting the following error.

C:\Python33\python.exe "C:/Users/koopt_000/Desktop/College/Sophomore Semester 2/Computer Science 231/Chapter7/Test.py"
Traceback (most recent call last):
 File "C:/Users/koopt_000/Desktop/College/Sophomore Semester 2/Computer Science 231/Chapter7/Test.py", line 16, in <module>
 print(BST.preOrder(tree))
TypeError: preOrder() missing 1 required positional argument: 'tree'
Process finished with exit code 1

I'm trying to print out my pre order of my tree and it just doesn't want to work, here is my code.

class TreeNode(object):
 def __init__(self, data = None, left=None, right=None):
 self.item = data
 self.left = left
 self.right = right
 def __str__(self):
 return str(self.item)
#------------------------------------------------------------
from TreeNode import TreeNode
class BST(object):
 #------------------------------------------------------------
 def __init__(self):
 self.root = None
 self.size = 0
 #------------------------------------------------------------
 def preOrder(self, tree):
 if tree is None:
 pass
 else:
 print(tree.item)
 preOrder(tree.left)
 preOrder(tree.right)
 def postOrder(self, root):
 if root is None:
 pass
 else:
 self.postOrder(root.left)
 self.postOrder(root.right)
 print(root.item)
 def inOrder(self, root):
 if root is None:
 pass
 else:
 self.inOrder(root.left)
 print(root.item)
 self.inOrder(root.right)

Here is my testing code:

from BinarySearchTree import BST
from TreeNode import TreeNode
tree = TreeNode(1,
 TreeNode(2,
 TreeNode(4,
 TreeNode(7,None,None),
 None),
 TreeNode(5, None, None)),
 TreeNode(3,
 TreeNode(6,
 TreeNode(8, None, None),
 TreeNode(9, None, None)),
 None))
print(BST.preOrder(tree))

I know it has to do something with me putting something for 'self' in my print statement, but I'm pretty stumped and my brain is not functioning properly at the moment. Any ideas?

Answer 1

Worked fine for me with some changes.

bst.py:

class TreeNode(object):
 def __init__(self, data = None, left=None, right=None):
 self.item = data
 self.left = left
 self.right = right
 def __str__(self):
 return str(self.item)
#------------------------------------------------------------
class BST(object):
 #------------------------------------------------------------
 def __init__(self):
 self.root = None
 self.size = 0
 #------------------------------------------------------------
 def preOrder(self, tree):
 if tree is None:
 pass
 else:
 print(tree.item)
 self.preOrder(tree.left)
 self.preOrder(tree.right)
 def postOrder(self, root):
 if root is None:
 pass
 else:
 self.postOrder(root.left)
 self.postOrder(root.right)
 print(root.item)
 def inOrder(self, root):
 if root is None:
 pass
 else:
 self.inOrder(root.left)
 print(root.item)
 self.inOrder(root.right)

something.py

from bst import BST
from bst import TreeNode
tree = TreeNode(1,
 TreeNode(2,
 TreeNode(4,
 TreeNode(7,None,None),
 None),
 TreeNode(5, None, None)),
 TreeNode(3,
 TreeNode(6,
 TreeNode(8, None, None),
 TreeNode(9, None, None)),
 None))
a = BST()
print(a.preOrder(tree))

Output:

bob@squids:~/Desktop$ python something.py
1
2
4
7
5
3
6
8
9
None