遍历二叉树 python

#coding=UTF-8

class Node:
    def __init__(self,value=None,left=None,right=None):
        self.value = value
        self.left = left
        self.right = right

#前序遍历
def preTraverse(root):
    if root ==None:
        return None
    print root.value
    preTraverse(root.left)
    preTraverse(root.right)

#中序遍历
def midTraverse(root):
    if root ==None:
        return None
    midTraverse(root.left)
    print root.value
    midTraverse(root.right)

#后序遍历
def afterTraverse(root):
    if root ==None:
        return None
    afterTraverse(root.left)
    afterTraverse(root.right)
    print root.value

#如果知道二叉树的前序遍历和中序遍历，求这棵二叉树的后序遍历
def findTree(preList,midList,afterList):
    if len(preList)==0:
        return
    if len(preList)==1:
        afterList.append(preList[0])
        return
    root=preList[0]
    n=midList.index(root)
    findTree(preList[1:n+1],midList[:n],afterList)
    findTree(preList[n + 1:], midList[n + 1:], afterList)
    afterList.append(root)
    return afterList

if __name__=='__main__':
    root = Node('D',Node('B',Node('A'),Node('C')),Node('E',right=Node('G',Node('F'))))
    print '前序遍历'
    preTraverse(root)
    print '中序遍历'
    midTraverse(root)
    print '后序遍历'
    afterTraverse(root)

    preList = list('DBACEGF')
    midList = list('ABCDEFG')
    afterList = []
    print findTree(preList,midList,afterList)