Question

在python（v3.6.1）中，我希望编写一个这样的类：

class SecondClass(FirstClass):
    property = "custom"

print(SecondClass.name) #=> "john"

class SecondClass(FirstClass):
    property = "notcustom"

print(SecondClass.name) #=> "steve"

我试图像这样设置FirstClass类：

class FirstClass:
    if property == "custom":
        name = "john"
    else:
        name = "steve"

但我似乎无法从SecondClass编辑FirstClass的属性。

这可能吗？

Answer 1

由于您使用的是Python 3.6，因此您可以使用新的__init_subclass__方法完成您的要求。来自__init_subclass__的文档：

只要包含类是子类，就会调用此方法。然后cls是新的子类。如果定义为普通实例方法，则此方法将隐式转换为类方法。

class FirstClass:
    def __init_subclass__(cls):
        super().__init_subclass__()
        if cls.property == "custom":
            cls.name = "john"
        else:
            cls.name = "steve"

class SecondClass(FirstClass):
    property = "custom"

print(SecondClass.name)

class SecondClass(FirstClass):
    property = "notcustom"

print(SecondClass.name)

对于适用于Python 3.5及更低版本的方法，您可以使用一些Meta类魔法：

class FirstClass(type):
    def __init__(cls, name, bases, attrs):
        if cls.property == "custom":
            cls.name = "john"
        else:
            cls.name = "steve"
        super(FirstClass, cls).__init__(name, bases, attrs)

class SecondClass(metaclass=FirstClass):
    property = "custom"

print(SecondClass.name)

class SecondClass(metaclass=FirstClass):
    property = "notcustom"

print(SecondClass.name)

Answer 2

@classmethod可能是您最好的选择。

class First:
    @classmethod
    def name(cls):
        return "john" if cls.prop() == "custom" else "steve"

class Second(First):
    @classmethod
    def prop(cls):
        return "custom"

print(Second.name()) # -> john

class Second(First):
    @classmethod
    def prop(cls):
        return "notcustom"

print(Second.name()) # -> steve

（另外，请勿使用property，因为它已经是语言中的关键字

Python：从子类更改父类属性

2 个答案: