maxDepth(tree).py

from collections import deque


def maxDepthLv(root):
    max_depth = 0
    if root is None:
        return max_depth
    q = deque()
    q.append((root, 1))
    while q:
        cur_node, cur_depth = q.popleft()
        max_depth = max(max_depth, cur_depth);
        if cur_node.left:
            q.append((cur_node.left, cur_depth + 1))
        if cur_node.right:
            q.append((cur_node.right, cur_depth + 1))
    return max_depth;

def maxDepthPost(root):
    max_depth = 0
    if root is None:
        return max_depth
    left_depth = maxDepthPost(root.left)
    right_depth = maxDepthPost(root.right)
    max_depth =  max(left_depth,right_depth) + 1;
    return max_depth

class TreeNode:
    def __init__(self, l = None, r = None , v = 0):
        self.left = l
        self.right = r
        self.value = v
        
root = TreeNode(v = 3)
root.left = TreeNode(v=9)
root.right = TreeNode(v=20)
root.right.left = TreeNode(v=15)
root.right.right = TreeNode(v=7)
print(maxDepthPost(root))