leetcode Maximum Depth of Binary Tree python

# Definition for a binary tree node.
# class TreeNode(object):
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution(object):
def maxDepth(self, root):
"""
:type root: TreeNode
:rtype: int
"""
if root == None:
return 0
if root.left == None and root.right != None:
return self.maxDepth(root.right)+1
if root.left != None and root.right == None:
return self.maxDepth(root.left)+1
return max(self.maxDepth(root.left),self.maxDepth(root.right))+1