iterator_pattern.py

#!/usr/bin/env python
# -*- coding:utf-8 -*-

__author__ = 'Andy'
"""
大话设计模式
设计模式——迭代器模式
迭代器模式(Iterator Pattern):提供方法顺序访问一个聚合对象中各元素，而又不暴露该对象的内部表示.
"""
#迭代器抽象类
class Iterator(object):
	def First(self):
		pass

	def Next(self):
		pass

	def Isdone(self):
		pass

	def CurrItem(self):
		pass

#聚集抽象类
class Aggregate(object):

	def CreateIterator(self):
		pass

#具体迭代器类
class ConcreteIterator(Iterator):

	def __init__(self, aggregate):
		self.aggregate = aggregate
		self.curr = 0

	def First(self):
		return self.aggregate[0]

	def Next(self):
		ret = None
		self.curr += 1
		if self.curr < len(self.aggregate):
			ret = self.aggregate[self.curr]
		return ret

	def Isdone(self):
		return True if self.curr+1 >= len(self.aggregate) else False

	def CurrItem(self):
		return self.aggregate[self.curr]

#具体聚集类
class ConcreteAggregate(Aggregate):

	def __init__(self):
		self.ilist = []

	def CreateIterator(self):
		return ConcreteIterator(self)

class ConcreteIteratorDesc(Iterator):
	def __init__(self, aggregate):
		self.aggregate = aggregate
		self.curr = len(aggregate)-1

	def First(self):
		return self.aggregate[-1]

	def Next(self):
		ret = None
		self.curr -= 1
		if self.curr >= 0:
			ret = self.aggregate[self.curr]
		return ret

	def Isdone(self):
		return True if self.curr-1<0 else False

	def CurrItem(self):
		return self.aggregate[self.curr]

if __name__=="__main__":
	ca = ConcreteAggregate()
	ca.ilist.append("大鸟")
	ca.ilist.append("小菜")
	ca.ilist.append("老外")
	ca.ilist.append("小偷")

	itor = ConcreteIterator(ca.ilist)
	print itor.First()
	while not itor.Isdone():
		print itor.Next()
	print "————倒序————"
	itordesc = ConcreteIteratorDesc(ca.ilist)
	print itordesc.First()
	while not itordesc.Isdone():
		print itordesc.Next()