Question

Really sorry for the extremely stupid title, but if I know what it is, I wouldn’t write here (:

def some_decorator( func ):
    # ..

class A:
    @some_decorator
    def func():
        pass
    @func.some_decorator    # this one here - func.some_decorator ?
    def func():
        pass

some_decorator decorates func – that’s OK. But what is func.some_decorator and how some_decorator becomes a member ( or something else ? ) of func?

P.S. I’m 90% sure, that there’s such question here (as this seems something basic), but I don’t know how to search it. If there’s a exact duplicate, I’ll delete this question.

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Note : It’s not typo, nor accident, that both member functions are named func. The decorator is for overloading: the question is related to Decorating method (class methods overloading)

Answer 1

Remember that the function definition with decorator is equivalent to this:

def func():
    pass
func = some_decorator(func)

So in the following lines, func doesn’t refer to the function you defined but to what the decorator turned it into. Also note that decorators can return any object, not just functions. So some_decorator returns an object with a method (it’s unfortunate that the names some_decorator and func are reused in the example – it’s confusing, but doesn’t change anything about the concept) that is itself a decorator. As the expression after the @ is evaluated first, you still have a reference to the first decorator’s method after you defined another plain function func. That decorator is applied to this new function. The full example is then equivalent to this:

class A:
    def func():
        pass
    func = some_decorator(func)

    _decorator = func.some_decorator
    def func():
        pass
    func = _decorator(func)