如何确定一个类的classmethod和staticmethod属性？

Question

在迭代类的属性时，我可以看到@classmethod 和@staticmethod 属性，但我不确定如何根据它们的类型通用地识别它们

class DeprecatedClassWithInit(object):
    def __init__(self):
        pass

    def foo(self):
        return "DeprecatedClassWithInit.foo()"

    @classmethod
    def bar(cls):
        return "DeprecatedClassWithInit.bar(cls)"

    @staticmethod
    def bab():
        return "DeprecatedClassWithInit.bab()"

属性看起来像：

bab = <function bab at 0x7f354f5711b8> (type = <type 'function'>)
bar = <bound method type.bar of <class 'utils.test_decorators.DeprecatedClassWithInit'>> (type = <type 'instancemethod'>)
foo = <unbound method DeprecatedClassWithInit.foo> (type = <type 'instancemethod'>)

所以实例方法有一个str() == "<unbound method DeprecatedClassWithInit.foo>" 而classmethod有str() == "<bound method type.bar of <class ...>>"
而staticmethod有str() == <function bab at 1232455>

这是识别属性的好方法吗？

Answer 1

不，您不应该依赖这些属性的字符串表示。相反，请注意classmethod 和staticmethod 是类型，即它们是类对象。对于那些想知道的人，它们被实现为描述符。只需遍历一个类的属性并使用isinstance：

class DeprecatedClassWithInit(object):
    def __init__(self):
        pass

    def foo(self):
        return "DeprecatedClassWithInit.foo()"

    @classmethod
    def bar(cls):
        return "DeprecatedClassWithInit.bar(cls)"

    @staticmethod
    def bab():
        return "DeprecatedClassWithInit.bab()"

for name, attr in vars(DeprecatedClassWithInit).items():
    if isinstance(attr, classmethod):
        print(name, "is a classmethod")
    elif isinstance(attr, staticmethod):
        print(name, "is a staticmethod")