如何从 __get__ 中获取描述符的属性名称？

Question

实现描述符时，可以使用__set_name__注册描述符设置在哪个属性名下。

虽然，假设我们要为同一个描述符设置多个属性，那么似乎没有办法知道在 __get__ 和 __set__ 中通过哪个名称访问描述符方法。

代码

class Prop:
    def  __init__(self):
        self._names = {}

    def __set_name__(self, owner, name):
        print(f'Attribute \'{name}\' was set to a Prop')

        if owner in self._names:
            self._names[owner].append(name)
        else:
            self._names[owner] = [name]

    def __get__(self, instance, owner):
        print(f'Prop was accessed through one of those: {self._names[owner]}')

prop = Prop()

class Foo:
    bar = prop
    baz = prop

foo = Foo()
foo.baz

输出

Attribute 'bar' was set to a Prop
Attribute 'baz' was set to a Prop
Prop was accessed through one of those: ['bar', 'baz']

是否有一种清晰通用的方法来了解从哪个属性访问了描述符？

Answer 1

Is there a clean and general way to know from which attribute a descriptor was accessed?

不，没有干净通用的方法。

然而，如果你想要一个肮脏的 hack（请不要那样做！）你可以避免描述符协议并只传递手动访问它的名称：

class Descriptor:
    def __get__(self, instance, owner, name=None):
        print(f"Property was accessed through {name}")
        return 'foo'

p = Descriptor()

class Test:
    a = p
    b = p

    def __getattribute__(self, name):
        for klass in type(self).__mro__:
            if name in klass.__dict__ and isinstance(klass.__dict__[name], Descriptor):
                return klass.__dict__[name].__get__(self, klass, name)
        else:
            return object.__getattribute__(self, name)