fix format error

codes/python/include/binary_tree.py

@@ -10,9 +10,19 @@ class TreeNode:
     """Definition for a binary tree node
     """    
     def __init__(self, val=None, left=None, right=None):
-        self.val = val
-        self.left = left
-        self.right = right
+        self.val = val  # 结点值
+        self.height = 0  # 结点高度, avl 树会用到
+        self.left = left  # 左子结点引用
+        self.right = right  # 右子结点引用
+
+    def __str__(self):  # 直接print时会好看一点
+        val = self.val
+        left_node_val = self.left.val if self.left else None
+        right_node_val = self.right.val if self.right else None
+        return "<TreeNode: {}, leftTreeNode: {}, rightTreeNode: {}>".format(val, left_node_val, right_node_val)
+
+    __repr__ = __str__
+
 
 def list_to_tree(arr):
     """Generate a binary tree with a list