Getting return values from a class

Question

How would I get return values in this case. (as I would a function)

class A(object):
    def __init__(self,a,b):
        self.a = a
        self.b = b
        self.run()
    def run(self):
        return a + b

When I do that I get an instance, how would I get a return value?

Thanks James

Answer 1

Are you trying to do something like:

class A(object):
    def __init__(self,a,b):
        self.a = a
        self.b = b
    def __call__(self):
        return self.a + self.b

a = A(3, 4)
a() # returns 7

It's not clear what you want and why. __init__ modifies the self object, but is required to return None (i.e. no return). Anything else will cause a TypeError.

EDIT: To avoid creating an instance, you can override __new__:

class A(object):
    def __new__(self,a,b):
        return A.run(a, b);
    @staticmethod
    def run(a, b):
        return a + b

You still haven't quite explained why you need this.

Answer 2

The main purpose of calling a type is to create (and return) an instance of that type -- though you may play tricks with __new__ to work around that, why, in the name of everything that matters, would you want to code a type that's intrinsically impossible to instantiate by the normal means?! Looks like you have something "clever" in mind, but, remember, "clever" is not a compliment in the Python community... rather, Python is about simplicity. Just use a function (or any other callable, e.g. an instance of a class with a __call__ method, for advanced but still quite reasonable use cases)!