Python: How can i decorate function to change it into class method

Question

I have code like this and i want to write decorator which will add decoradted function as class method of class A.

class A:
    pass

@add_class_method(A)
def foo():
    return "Hello!"

@add_instance_method(A)
def bar():
    return "Hello again!"

assert A.foo() == "Hello!"
assert A().bar() == "Hello again!"

It seems like the author wants to dynamically add a classmethod — ekon, Apr 27 '21 at 14:04
I don't think so. I guess it has to be just method of the class not @classmethod — koliber, Apr 27 '21 at 14:04

score 1 · Accepted Answer · answered Apr 27 '21 at 14:46

What about this approach?
P.S. The code is not structurally optimized for the sake of clarity

from functools import wraps


class A:
    pass


def add_class_method(cls):
    def decorator(f):
        @wraps(f)
        def inner(_, *args, **kwargs):
            return f(*args, **kwargs)

        setattr(cls, inner.__name__, classmethod(inner))

        return f

    return decorator


def add_instance_method(cls):
    def decorator(f):
        @wraps(f)
        def inner(_, *args, **kwargs):
            return f(*args, **kwargs)

        setattr(cls, inner.__name__, inner)

        return f

    return decorator


@add_class_method(A)
def foo():
    return "Hello!"


@add_instance_method(A)
def bar():
    return "Hello again!"


assert A.foo() == "Hello!"
assert A().bar() == "Hello again!"

Thank you <3. Could you just tell me what is this "_" inside inner pls. Sorry for my bad english btw. — koliber, Apr 27 '21 at 14:54
[This](https://stackoverflow.com/a/5893946/11179620) answer explains it well enough — ekon, Apr 27 '21 at 14:57

score 0 · Answer 2 · answered Apr 27 '21 at 14:10

0

Is this what You were going for:

class A:
    def __init__(self):
        pass

    @classmethod
    def foo(cls):
        return "Hello!"

    def bar(self):
        return "Hello again!"


print(A.foo())
print(A().bar())

answered Apr 27 '21 at 14:10

Matiiss

5,970
2
12
29

Not really, i have to write code of these two decorators: add_class_method and add_instance_method. This code is just an example of how the result should look like. – koliber Apr 27 '21 at 14:13

score 0 · Answer 3 · answered Apr 27 '21 at 14:26

0

read docs here

class MyClass:
    def method(self):
        # instance Method
        return 'instance method called', self

    @classmethod
    def cls_method(cls):
        #Classmethod
        return 'class method called', cls

    @staticmethod
    def static_method():
        # static method
        return 'static method called'

You need to instantiate MyClass To reach(Call) Instance Method

test = MyClass()
test.method()

You Can directly access class Method without instantiate

MyClass.cls_method()
MyClass.static_method()

answered Apr 27 '21 at 14:26

George Imerlishvili

1,816
2
12
20

But my class should be empty at the beginning, and i have to add method foo and bar via these decorators def add_class_method(A): def real_decorator(func): def wrapper(*args,**kwargs): return func(*args, **kwargs) return wrapper() return real_decorator I have passed class to decorator but i dont know how to return it with intended method – koliber Apr 27 '21 at 14:45

Python: How can i decorate function to change it into class method

3 Answers3