binaryTree.py

class TreeNode:

 def __init__(self, key):
 self.left = None
 self.right = None
 self.key = key

def is_bst(root):
 result = False
 min = float('-inf')
 max = float('inf')

 return is_bst_recursive(root, min, max)

def is_bst_recursive(root, min, max):

 result = False

 result = root == None or (
 isRootKeyValid(root, min, max) and \
 is_bst_recursive(root.left, min, root.key-1) and \
 is_bst_recursive(root.right, root.key + 1, max))

 return result

def isRootKeyValid(root, min, max):
 return root.key >= min and root.key <= max