python decorator for class method and static method?

Question

I am trying to write a decorator for an instance method, as follows:

from functools import wraps

def plus_decorator(f):
    @wraps(f)
    def wrapper(*args, **kwargs):
        return 1 + f(*args, **kwargs)
    return wrapper

@plus_decorator
def return_i(i):
    return i

class A(object):
    @plus_decorator
    def return_i(self, i):
        return i

    @plus_decorator
    @classmethod
    def return_i_class(cls, i):
        return i

    @plus_decorator
    @staticmethod
    def return_i_static(i):
        return i

if __name__ == '__main__':
    print return_i(1)
    a = A()
    print a.return_i(1)
    print A.return_i_class(1)
    print A.return_i_static(1)

However, it pops up the error:

AttributeError: 'classmethod' object has no attribute '__module__'

I am wondering why the decorator does not work on classmethod and staticmethod. I think the decorator mostly just passes all the parameters it receives to the wrapper, and only modifies the result. How can I modify the decorator to make it work for classmethod and staticmethod?

This works fine. You aren't creating an instance of A() to call it, e.g. a = A(); a.return_i(1). Perhaps you also need @classmethod? — AChampion
– AChampion, Commented Jul 13, 2017 at 1:54
Oops. The original error I met was decorator for class method, and somehow I messed up the callsite for instance method. Let me change the content. — Justin Li
– Justin Li, Commented Jul 13, 2017 at 1:59

Dietrich Epp · Accepted Answer · 2017-07-13 02:05:20Z

9

Just flip the order. Put the @classmethod or @staticmethod on the outside, and your decorator (which uses @wraps, and therefore needs a bare function) on the inside.

@classmethod
@plus_decorator
def return_i_class(cls, i):
    return i

answered Jul 13, 2017 at 2:05

Dietrich Epp

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Comments

Yug Shende · Accepted Answer · 2017-07-13 02:07:32Z

3

Try reversing.

It will work when @staticmethod and @classmethod are top-most decorators as explained here

Because your decorator expects a function but both the other decorators return descriptor objects.

answered Jul 13, 2017 at 2:07

Yug Shende

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