Question

我已经获得了这本书的副本＆＃34; Head First Design Patterns＆＃34;并开始用Python编写他们的一些例子。我已经看到了关于Decorator模式的例子，我知道它应该使用组合，但作者提出了一种继承＆＃34;。借口是装饰器是为了实现类型匹配，而不是用来继承行为＆＃34;。我在这里有一个问题，我知道Python不是一种打字语言，所以当我从书中的例子（使用Java）时，我得到了这个：

from abc import ABCMeta, abstractmethod

class Beverage:
    __metaClass__=ABCMeta

    def __init__(self):
        self.Description="Beverage desconocida"

    def getDescription(self):
        return self.Description

    @abstractmethod
    def calc(self):
        pass


class CondimentDecorator(Beverage):
    __metaClass__=ABCMeta

    @abstractmethod
    def getDescription(self):
        pass

class Espresso(Beverage):
    def __init__(self):
        self.Description="Espresso"

    def calc(self):
        return 2.5

class Pasado(Beverage):
    def __init__(self):
        self.Description="Roasted coffee"

    def calc(self):
        return 1.5

class Mocha(CondimentDecorator):
    def __init__(self,Beverage):
        self.Beverage=Beverage

    def getDescription(self):
        return self.Beverage.getDescription()+" Mocha "

    def calc(self):
        return 0.5+self.Beverage.calc()

def main():
    Beverage=Espresso()
    print Beverage.getDescription()," cost: ",Beverage.calc()
    Beverage2=Pasado()
    Beverage2=Mocha(Beverage2)
    print Beverage2.getDescription()," cost: ",Beverage2.calc()
    Beverage3=Espresso()
    Beverage3=Mocha(Mocha(Beverage3))
    print Beverage3.getDescription()," cost: ",Beverage3.calc()

我想知道是否上课：

CondimentDecorator（饮料）

做得好，因为只要Python没有类型，我就不需要继承Beverage;我是对的吗？

如果我改变它：

CondimentDecorator（），我的代码仍然有效，但在这种情况下，我想知道它是否有必要拥有它，因为它只有一个抽象方法而且它就是它。

我是否需要更改我的代码以使其与Python OOP编程更加一致？

由于

Answer 1

Python没有严格的输入，通常不需要继承或抽象类。装饰器模式需要Decorator-Class，因为它应该定义装饰类的每个方法来调用嵌入式实例的方法。如果你覆盖所有方法，你绝对不需要这个装饰类。这是一个没有继承的版本：

class Espresso(object):
    description="Espresso"

    def calc(self):
        return 2.5

class Pasado(object):
    description="Roasted coffee"

    def calc(self):
        return 1.5

class Mocha(object):
    def __init__(self, beverage):
        self.beverage = beverage

    @property
    def description(self):
        return self.beverage.description+" Mocha"

    def calc(self):
        return 0.5+self.beverage.calc()

def main():
    beverage = Espresso()
    print beverage.description, " cost: ", beverage.calc()
    beverage2 = Pasado()
    beverage2 = Mocha(beverage2)
    print beverage2.description, " cost: ", beverage2.calc()
    beverage3 = Espresso()
    beverage3 = Mocha(Mocha(beverage3))
    print beverage3.description, " cost: ", beverage3.calc()

if __name__ == '__main__':
    main()

另一方面，Python是一种动态语言，您可以编写动态装饰器

class GenericDecorator（object）： def init （self，obj）： self.obj = obj

    def __getattr__(self, name):
        return getattr(self.obj, name)

class Flavored(GenericDecorator):
    """Flavor is for free"""
    def __init__(self, beverage, flavor):
        GenericDecorator.__init__(self, beverage)
        self.flavor = flavor

    @property
    def description(self):
        return self.flavor + '-' + self.obj.description

def main():
    beverage = Espresso()
    beverage = Flavored(beverage, 'Vanilla')
    print beverage.description, " cost: ", beverage.calc()

if __name__ == '__main__':
    main()

如何将这个装饰器改成Python？

1 个答案: