在python中使用@property的正确方法是什么

Question

我有以下代码，Dog 和 Cat 类是从 Animal 类继承的。 Person 类使用 Dog 和 Cat 类作为其实例。我想要返回实例名称的函数，如字符串“get the name xxx”，用于 john 实例和 john 的属性狗、猫的名字。我试图在 Animal 类和 Person 下编写属性 namegetter ，我可以得到我想要的。但是，是否有适当的方法来做到这一点？所以如果我有几个像 Person 这样的类，我不需要在类下写相同的属性

class Animal(object):
    def __init__(self, name):
        self.name = name

    @property
    def namegetter(self):
        return 'get the name of {}'.format(self.name)

class Cat(Animal):
    def __init__(self, food, name):
        super().__init__(name)
        self.food = food
        self.sound = 'meow'

class Dog(Animal):
    def __init__(self, food, name):
        super().__init__(name)
        self.food = food
        self.space = 'park'


class Person(object):

    def __init__(self, name):
        self.name = name
        self.dog = Dog("dog's food", "dog's name" )
        self.cat = Cat("dog's food", "cat's name")

    @property
    def namegetter(self):
        return 'get the name of {}'.format(self.name)

if __name__ == '__main__':
    john = Person('john')
    print(john.name) #john
    print(john.dog.name) #dog's name
    print(john.cat.name) #cat's name
    print(john.dog.namegetter) #get the name of dog
    print(john.cat.namegetter) #get the name of cat
    print(john.namegetter) #get the name of john

Answer 1

基于 cmets，我猜你想避免两次定义相同的方法。 您可以使用 Mixins（在复杂的层次结构中）或仅使用另一个基类来做到这一点。至于你是否可以避免写@property的问题：你可以不写，但是你必须在你的方法后面写大括号namegetter()。

使用基类的示例：

class NamedEntity(object):
    def __init__(self, name):
        self.name = name

    @property
    def namegetter(self):
        return 'get the name of {}'.format(self.name)


class Animal(NamedEntity):
    pass


class Cat(Animal):
    def __init__(self, food, name):
        super(Cat, self).__init__(name)
        self.food = food
        self.sound = 'meow'


class Dog(Animal):
    def __init__(self, food, name):
        super(Dog, self).__init__(name)
        self.food = food
        self.space = 'park'


class Person(NamedEntity):

    def __init__(self, name):
        super(Person, self).__init__(name)
        self.dog = Dog("dog's food", "dog's name" )
        self.cat = Cat("dog's food", "cat's name")


if __name__ == '__main__':
    john = Person('john')
    print(john.name) #john
    print(john.dog.name) #dog's name
    print(john.cat.name) #cat's name
    print(john.dog.namegetter) #get the name of dog
    print(john.cat.namegetter) #get the name of cat
    print(john.namegetter) #get the name of john

在一个更复杂的例子中，你可以使用 Mixin，这基本上会改变你在类定义中从它继承的方式：

class NamedEntityMixin(object):
    def __init__(self, name):
        self.name = name

    @property
    def namegetter(self):
        return 'get the name of {}'.format(self.name)


class Animal(NamedEntityMixin, object):
    # Imagine object being another parent class with additional properties and methods
    pass


class Cat(Animal):
    def __init__(self, food, name):
        super(Cat, self).__init__(name)
        self.food = food
        self.sound = 'meow'


class Dog(Animal):
    def __init__(self, food, name):
        super(Dog, self).__init__(name)
        self.food = food
        self.space = 'park'


class Person(NamedEntityMixin, object):
    # Imagine object being another parent class with additional properties and methods
    def __init__(self, name):
        super(Person, self).__init__(name)
        self.dog = Dog("dog's food", "dog's name" )
        self.cat = Cat("dog's food", "cat's name")


if __name__ == '__main__':
    john = Person('john')
    print(john.name) #john
    print(john.dog.name) #dog's name
    print(john.cat.name) #cat's name
    print(john.dog.namegetter) #get the name of dog
    print(john.cat.namegetter) #get the name of cat
    print(john.namegetter) #get the name of john

二传手

在 cmets 中，您询问如果有人想写信给 namegetter 怎么办。上面，我只定义了只读访问，因为namegetter 这个名字在我听来好像你需要它。下面，我为您定义了一个带有 getter 和 setter 的版本，它允许您使用可选变量 {name} 按需替换来设置格式字符串：

class NamedEntity(object):
    def __init__(self, name):
        self.name = name
        self._namegetter = "get the name of {name}"

def _get_namegetter(self):
    return self._namegetter.format(name=self.name)

def _set_namegetter(self, namegetter):
    self._namegetter = namegetter

namegetter = property(_get_namegetter, _set_namegetter)


class Animal(NamedEntity):
    pass


class Cat(Animal):
    def __init__(self, food, name):
        super(Cat, self).__init__(name)
        self.food = food
        self.sound = 'meow'
        self.namegetter = 'catnamegetter'


class Dog(Animal):
    def __init__(self, food, name):
        super(Dog, self).__init__(name)
        self.food = food
        self.space = 'park'


class Person(NamedEntity):

    def __init__(self, name):
        super(Person, self).__init__(name)
        self.dog = Dog("dog's food", "dog's name" )
        self.cat = Cat("dog's food", "cat's name")


if __name__ == '__main__':
    john = Person('john')
    print(john.name) #john
    print(john.dog.name) #dog's name
    print(john.cat.name) #cat's name
    print(john.dog.namegetter) #get the name of dog
    print(john.cat.namegetter) #get the name of cat
    print(john.namegetter) #get the name of john

我将 getter 和 setter 拆分为两个方法，并将它们作为 namegetter 属性提供。 Python 会根据你自动访问属性的方式选择正确的方法。

然而，上述解决方案不再使用装饰器，这可能会降低代码的可读性。带有装饰器的版本是这个。请注意，namegetter 方法使用不同的装饰器定义了两次：

class NamedEntity(object):
    def __init__(self, name):
        self.name = name
        self._namegetter = "get the name of {name}"

    @property
    def namegetter(self):
        return self._namegetter.format(name=self.name)

    @namegetter.setter
    def namegetter(self, namegetter):
        self._namegetter = namegetter



class Animal(NamedEntity):
    pass


class Cat(Animal):
    def __init__(self, food, name):
        super(Cat, self).__init__(name)
        self.food = food
        self.sound = 'meow'
        self.namegetter = 'catnamegetter'


class Dog(Animal):
    def __init__(self, food, name):
        super(Dog, self).__init__(name)
        self.food = food
        self.space = 'park'


class Person(NamedEntity):

    def __init__(self, name):
        super(Person, self).__init__(name)
        self.dog = Dog("dog's food", "dog's name" )
        self.cat = Cat("dog's food", "cat's name")


if __name__ == '__main__':
    john = Person('john')
    print(john.name) #john
    print(john.dog.name) #dog's name
    print(john.cat.name) #cat's name
    print(john.dog.namegetter) #get the name of dog
    print(john.cat.namegetter) #get the name of cat
    print(john.namegetter) #get the name of john