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()