如何使用条件重写方法

使用元类和继承的干净解决方案:

class AnimalType(type):
    _classes = {}

    def __init__(cls, name, attribs, bases):
        super(AnimalType, cls).__init__(name, attribs, bases)
        cls._classes[name.lower()] = cls


class Animal(object):
    __metaclass__ = AnimalType

    def __new__(cls, name=None):
        newcls = type(cls)._classes.get(name, Animal)
        return object.__new__(newcls, name)

    def __init__(self, name=None):
        self.name = name

    def execute(self):
        print("I am animal")


class Dog(Animal):
    def execute(self):
        print("I am a dog")


class Cat(Animal):
    def execute(self):
        print("I am a cat")

如果您根本不想继承,只需使用工厂函数:

class Animal(object):
    def execute(self):
        print("I am animal")

class Dog:
    def execute(self):
        print("I am a dog")

class Cat:
    def execute(self):
        print("I am a cat")


_clsmap = {
   "animal": Animal,
   "dog": Dog,
   "cat": Cat
   }

def make_animal(name):
    return _clsmap.get(name, Animal)()

虽然继承是这里的最佳解决方案,但OP特别要求另一种解决方案

object = Dog() 或 object = Cat() Dog 或 Cat object 就这样。它与任何东西都没有关系。

Animal 捆绑 Animal.execute 适当的 execute 方法。

class Dog:
    def execute(self):
        print("I am a dog")

class Cat:
    def execute(self):
        print("I am a cat")

class Animal(object):
    names_to_classes = {'dog': Dog, 'cat': Cat}

    def __init__(self, name=None):
        self.name = name
        try:
            self.object = self.names_to_classes[name]()
        except KeyError:
            raise TypeError('name must be either "dog" or "cat"')

    def execute(self):
        self.object.execute()


instanceAnimal = Animal("cat")
instanceAnimal.execute()
instanceAnimal = Animal("dog")
instanceAnimal.execute()
instanceAnimal = Animal("penguin")
instanceAnimal.execute()

输出

I am a cat
I am a dog
TypeError: name must be either "dog" or "cat"

这种方法的缺点是 Dog.__init__ 和 Cat.__init__ 期望接受相同的参数。

以下是如何实现您的目标:

class Animal(object):
    def __init__(self, name=None):
        if name == 'cat':
            self._object = Cat()
        elif name == 'dog':
            self._object = Dog()
        else:
            self._object = None

    def execute(self):
        if self._object is not None:
            self._object.execute()
        else:
            print("I am animal")