用python抽象类实现单一职责原则

Question

我想将数据库模型与实际类分开。 但是无论子类类型如何，我都需要两个 static 函数来从数据库中获取数据。 这两个功能的实现在所有数据库模型中都是相同的。

pyright显示get()和get_all()函数中的cls没有db属性的错误。

from abc import ABC, abstractstaticmethod


class DogsDB:
    lists = ["DOG1", "DOG2", "DOG3"]

    @classmethod
    def get(cls, id):
        return cls.lists[id]


class CatsDB:
    lists = ["CAT1", "CAT2", "CAT3"]

    @classmethod
    def get(cls, id):
        return cls.lists[id]


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

    @abstractstaticmethod
    def save(m):
        pass

    @abstractstaticmethod
    def _from_model(obj):
        pass

    @classmethod
    def get(cls, id):
        obj = cls.db.get(id)
        return cls._from_model(obj)

    @classmethod
    def get_all(cls):
        objs = cls.db.lists

        lists = []
        for obj in objs:
            e = cls._from_model(obj)
            lists.append(e)
        return lists

    def __repr__(self):
        return self.name


class DogSound:
    def __init__(self, name):
        self.name = name

    def sound(self):
        print(self.name, ": DOG SOUND!!")


class Dog(Animal, DogSound):
    db = DogsDB

    def __init__(self, name, age):
        super(Dog, self).__init__(name)
        self.age = age

    @staticmethod
    def save(m):
        print(m)

    @staticmethod
    def _from_model(obj):
        return Dog(obj, 4)


class Cat(Animal):
    db = CatsDB

    def __init__(self,  name, age):
        super().__init__(name)
        self.age = age

    @staticmethod
    def save(m):
        print(m)

    @staticmethod
    def _from_model(obj):
        return Cat(obj, 4)


print(Cat.get(1))
print(Dog.get(1))
print(Cat.get_all())
print(Dog.get_all())
Dog.get(1).sound()

Answer 1

我无法复制您的第一个错误。

您的第二个问题是方法sound隐式返回None的结果，因为它没有 return 语句并且您有print(Dog.get(1).sound()) ，它将打印出该方法的返回值。 您要么想将其更改为仅Dog.get(1).sound() ，要么修改sound方法以返回当前正在打印的内容并删除print语句（我的选择）。

顺便说一句，我发现这个 class 结构有点难以理解。 为什么你需要一个单独的DogSound class 和一个应该属于Animal的name属性？ 另外，在我看来， age可能/应该是Animal的一个属性，因为猫和狗都有年龄。

from abc import ABC, abstractstaticmethod


class DogsDB:
    lists = ["DOG1", "DOG2", "DOG3"]

    @classmethod
    def get(cls, id):
        return cls.lists[id]


class CatsDB:
    lists = ["CAT1", "CAT2", "CAT3"]

    @classmethod
    def get(cls, id):
        return cls.lists[id]


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

    @abstractstaticmethod
    def save(m):
        pass

    @abstractstaticmethod
    def _from_model(obj):
        pass

    @classmethod
    def get(cls, id):
        obj = cls.db.get(id)
        return cls._from_model(obj)

    @classmethod
    def get_all(cls):
        objs = cls.db.lists

        lists = []
        for obj in objs:
            e = cls._from_model(obj)
            lists.append(e)
        return lists

    def __repr__(self):
        return self.name

class Dog(Animal):
    db = DogsDB

    def __init__(self, name, age):
        super().__init__(name, age)

    def sound(self):
        return f"{self.name}: DOG SOUND!!"

    @staticmethod
    def save(m):
        print(m)

    @staticmethod
    def _from_model(obj):
        return Dog(obj, 4)


class Cat(Animal):
    db = CatsDB

    def __init__(self,  name, age):
        super().__init__(name, age)
        self.age = age

    @staticmethod
    def save(m):
        print(m)

    @staticmethod
    def _from_model(obj):
        return Cat(obj, 4)


print(Cat.get(1))
print(Dog.get(1))
print(Cat.get_all())
print(Dog.get_all())
print(Dog.get(1).sound())

印刷：

CAT2
DOG2
[CAT1, CAT2, CAT3]
[DOG1, DOG2, DOG3]
DOG2: DOG SOUND!!

如果出于某种原因您希望DogSound成为一个单独的 class，则无需复制name属性：

...
class DogSound: # A "Mixin" class
    def sound(self):
        return f"{self.name}: DOG SOUND!!"


class Dog(Animal, DogSound):
    db = DogsDB

    def __init__(self, name, age):
        super().__init__(name, age)

    @staticmethod
    def save(m):
        print(m)

    @staticmethod
    def _from_model(obj):
        return Dog(obj, 4)
...