第9章 魔法方法、属性和迭代器

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构造方法：

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property函数

__metaclass__=type

class Rectangle:

    def __init__(self):

        self.hight=self.width=0

    def getSize(self):

        return self.width,self.hight

    def setSize(self,size):

        self.width,self.hight=size

    size=property(getSize,setSize)

 

a=Rectangle()

a.width=10

a.hight=5

print a.size

a.size=100,150

print a.width

 

静态方法和类成员方法

__metaclass__=type

class MyClass:

    def smeth():

        print 'this is a static method'

    smeth=staticmethod(smeth)

 

    def cmeth(cls):

        print 'this is a class method',cls

    cmeth=classmethod(cmeth)

 

print MyClass.smeth()

print MyClass.cmeth()

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用装饰器对上述方法进行修改：

__metaclass__=type

class MyClass:

    @staticmethod

    def smeth():

        print 'this is a smeth'

 

    @classmethod

    def cmeth(cls):

        print 'this is a cmeth'

 

print MyClass.smeth()

print MyClass.cmeth()

 

 

得到的结果都如下所示：

this is a smeth

None

this is a cmeth

None

 

迭代器

特殊方法__iter__是迭代器规则的基础。

       不仅可以对序列和字典进行迭代，也可以对其他的对象进行迭代：实现__iter__方法的对象。

 

从迭代器得到序列

使用list构造方法显式地将迭代器转化为列表

示例1：

示例2：

class Fibs:

    def __init__(self):

        self.a=0

        self.b=1

    def next(self):

        self.a,self.b=self.b,self.a+self.b

        if self.a > 50: raise StopIteration

        return self.a

    def __iter__(self):

        return self

 

fibs=Fibs()

a=list(fibs)

print a

 

生成器：

def flatten(netsted):

    for sublist in netsted:

        for a in sublist:

            yield a

 

netsted=[[1,2],[3,4],[7],9]

a=list(flatten(netsted))

print a

 

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递归生成器：

def fun(netsted):

    try:

        for sublist in netsted:

            for element in fun(sublist):

                yield element

    except TypeError:

        yield netsted

 

netsted=[[1,2],[3,5],[8,9],10]

a=list(fun(netsted))

print a

 

 

模拟生成器：

生成器在旧版本的Python中是不可用的，下面介绍的是如何使用普通函数模拟生成器。

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def fun(netsted):

    result=[]

    try:

        try:

            netsted + ''

        except TypeError:pass

        else: raise TypeError

        for sublist in netsted:

            for element in fun(sublist):

                result.append(element)

    except TypeError:

        result.append(netsted)

    return result

 

netsted=[1,2,3,4,5]

a=fun(netsted)

print a

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