Python decorator as a staticmethod

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I'm trying to write a python class which uses a decorator function that needs information of the instance state. This is working as intended, but if I explicitly make the decorator a staticmetod, I get the following error:

Traceback (most recent call last):
  File "tford.py", line 1, in <module>
    class TFord(object):
  File "tford.py", line 14, in TFord
    @ensure_black
TypeError: 'staticmethod' object is not callable

Why?

Here is the code:

class TFord(object):
    def __init__(self, color):
        self.color = color

    @staticmethod
    def ensure_black(func):
        def _aux(self, *args, **kwargs):
            if self.color == 'black':
                return func(*args, **kwargs)
            else:
                return None
        return _aux

    @ensure_black
    def get():
        return 'Here is your shiny new T-Ford'

if __name__ == '__main__':
    ford_red = TFord('red')
    ford_black = TFord('black')

    print ford_red.get()
    print ford_black.get()

And if I just remove the line @staticmethod, everything works, but I do not understand why. Shouldn't it need self as a first argument?

static-methods decorator python
4 Answers

Solution does exist!

Problem is that Static method that is trying to be used as decorator is in fact staticmethod object and is not callable.

Solution: staticmethod object has method __get__ which takes any argument and returns real method: python documentation Python 3.5 and up:

class StaticMethod(object):
    "Emulate PyStaticMethod_Type() in Objects/funcobject.c"

    def __init__(self, f):
        self.f = f

    def __get__(self, obj, objtype=None):
        return self.f

Min solution I came with is:

class A():
    def __init__(self):
        self.n =  2

    @staticmethod
    def _returnBaseAndResult(func):
        from functools import wraps
        @wraps(func)
        def wrapper(*args, **kwargs):
            self = args[0]
            response = func(*args, **kwargs)
            return self.n, response
        return wrapper

    @_returnBaseAndResult.__get__('this can be anything')
    def square(self):
        return self.n**2

if __name__ == '__main__':
    a = A()
    print(a.square())

Will print (2, 4)

user_78376280
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