本文實例講述了Python二叉樹定義與遍歷方法。分享給大家供大家參考，具體如下：

二叉樹基本概述：

二叉樹是有限個元素的幾個，如果為空則為空二叉樹，或者有一個結點稱之為根節點，分列根節點兩側的為二叉樹的左右子節點，二叉樹有如下的性質：

1. 二叉樹的每個結點不存在度大于2的結點
2. 二叉樹的第i層至多有2^{i-1}個結點
3. 深度為k的二叉樹至多有2^k - 1個結點
4. 二叉樹中，度為0的結點數N0比度為2的結點數N2大1，即存在N2 + 1 = N0

Python代碼：

#coding:utf-8'BiTree'class Node(object):  'Node Defination'  def __init__(self,item):    self.item = item    self.left = None    self.right = Noneclass Tree(object):  'Bitree Defination'  def __init__(self):    self.root = None  def add(self,item):    node = Node(item)    if self.root is None:      self.root = node    else:      q = [self.root]      while True:        pop_node = q.pop(0)        if pop_node.left is None:          pop_node.left = node          return        elif pop_node.right is None:          pop_node.right = node          return        else:          q.append(pop_node.left)          q.append(pop_node.right)  def traverse(self):#層次遍歷    if self.root is None:      return None    q = [self.root]    res = [self.root.item]    while q != []:      pop_node = q.pop(0)      if pop_node.left is not None:        q.append(pop_node.left)        res.append(pop_node.left.item)      if pop_node.right is not None:        q.append(pop_node.right)        res.append(pop_node.right.item)    return res  def preorder(self,root): #先序遍歷    if root is None:      return []    result = [root.item]    left_item = self.preorder(root.left)    right_item = self.preorder(root.right)    return result + left_item + right_item  def inorder(self,root): #中序遍歷    if root is None:      return []    result = [root.item]    left_item = self.inorder(root.left)    right_item = self.inorder(root.right)    return left_item + result + right_item  def postorder(self,root): #后序遍歷    if root is None:      return []    result = [root.item]    left_item = self.postorder(root.left)    right_item = self.postorder(root.right)    return left_item + right_item + resultif __name__=='__main__':  t = Tree()  for i in range(10):    t.add(i)  print "層序遍歷:",t.traverse()  print "先序遍歷:",t.preorder(t.root)  print "中序遍歷:",t.inorder(t.root)  print "后序遍歷:",t.postorder(t.root)

輸出結果：

層序遍歷: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
先序遍歷: [0, 1, 3, 7, 8, 4, 9, 2, 5, 6]
中序遍歷: [7, 3, 8, 1, 9, 4, 0, 5, 2, 6]
后序遍歷: [7, 8, 3, 9, 4, 1, 5, 6, 2, 0]

這里對于

if __name__=='__main__':“Make a script both importable and executable”

意思就是說讓你寫的腳本模塊既可以導入到別的模塊中用，另外該模塊自己也可執行。