validates whether tree is binary search tree or not

is_binary_search_tree.py

""" Node is defined as
class node:
    def __init__(self, data):
        self.data = data
        self.left = None
        self.right = None
"""

def isBSTUtil(node, min, max):
    if node.data <= min:
            return False

    if node.data >= max:
        return False

    left_ok = True
    right_ok = True

    if node.left is not None:
        left_ok = isBSTUtil(node.left, min, node.data)
    if node.right is not None:
        right_ok = isBSTUtil(node.right, node.data, max)

    return left_ok and right_ok
    
def checkBST(root):
    if root is None:
        return True
    return (isBSTUtil(root, float('-inf'), float('inf')))