是否可以测试对象属性是否使用描述符？

Question

我不相信这是可能的，但我想我会问，因为我是 Python 新手。给定一个具有属性的对象，该属性的值由描述符处理；是否有可能知道涉及给定的描述符类型？

示例描述符：

class Column(object):
    def __init__(self, label):
        self.label = label

    def __get__(self, obj, owner):
        return obj.__dict__.get(self.label)

    def __set__(self, obj, value):
        obj.__dict__[self.label] = value

测试对象：

class Test(object):
    name = Column("column_name")

    def add(self):
       print self.name.__class__

执行此操作：

my_test = Test()
my_test.name = "myname"
my_test.add()  

这给出：<type 'str'> 这是值“myname”的数据类型，是否可以测试 isinstance(self.name, Descriptor) - 这返回 false，但我希望它返回 true - 或其他类似吗？

编辑 - 删除 Test 上旧式类的错误

Answer 1

按方法解析顺序搜索对象的类和超类以查找描述符对象：

def find_descriptor(instance, attrname):
    '''Find the descriptor handling a given attribute, if any.

    If the attribute named attrname of the given instance is handled by a
    descriptor, this will return the descriptor object handling the attribute.
    Otherwise, it will return None.
    '''
    def hasspecialmethod(obj, name):
        return any(name in klass.__dict__ for klass in type(obj).__mro__)
    for klass in type(instance).__mro__:
        if attrname in klass.__dict__:
            descriptor = klass.__dict__[attrname]
            if not (hasspecialmethod(descriptor, '__get__') or
                    hasspecialmethod(descriptor, '__set__') or
                    hasspecialmethod(descriptor, '__delete__')):
                # Attribute isn't a descriptor
                return None
            if (attrname in instance.__dict__ and
                not hasspecialmethod(descriptor, '__set__') and
                not hasspecialmethod(descriptor, '__delete__')):
                # Would be handled by the descriptor, but the descriptor isn't
                # a data descriptor and the object has a dict entry overriding
                # it.
                return None
            return descriptor
    return None