Python设计模式之迭代器模式原理与用法实例分析

#!/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()