Fine tune

codes/python/include/binary_tree.py

@@ -9,13 +9,13 @@ import collections
 class TreeNode:
     """Definition for a binary tree node
     """    
-    def __init__(self, val=None, left=None, right=None):
-        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
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val      # 结点值
+        self.height = 0     # 结点高度
+        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
+    def __str__(self):
         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