Python 求二叉树所有左叶节点的和

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 sumOfLeftLeaves(self, root):
        """
        :type root: TreeNode
        :rtype: int
        """
        if root is None or self.isleaf(root):
            return 0
        if self.isleaf(root.left):
            return root.left.val + self.sumOfLeftLeaves(root.right)
        else:
            return self.sumOfLeftLeaves(root.left) + self.sumOfLeftLeaves(root.right)
        
    def isleaf(self,root):
        return root.left is None and root.left is None

原题地址是 https://leetcode.com/problems/sum-of-left-leaves/ 求解，这段代码哪里写错了？