二叉树的先序遍历，中序遍历和后序遍历。

先序：根左右
中序：左根右
后序：左右根

class Btree():
	def __init__(self):
		self.data=None
		self.lchild=None
		self.rchild=None
####先序	
def printfontorder(tree,re=[]):
	if tree==None:
		return re
	else:
		re.append(tree.data)
		printfontorder(tree.lchild)
		printfontorder(tree.rchild)
	return re				
####中序
def printMidorder(tree):
	if tree==None:
		return None
	else:
		if tree.lchild!=None:
			printMidorder(tree.lchild)
		print(tree.data)
		if tree.rchild!=None:
			printMidorder(tree,rchild)
def  printMid2（tree,re=[]):
	if tree==None:
		return re
	else:
		printMid2(tree.lchild)
		re.append(tree.data)
		printMid2(tree.rchild)
	return re
#####后续
def  printrear（tree,re=[]):
	if tree==None:
		return re
	else:
		printMid2(tree.lchild)
		printMid2(tree.rchild)
		re.append(tree.data)
	return re