adder.py

class Two(object):
    
    def __init__(self, x, y):
        self.x = x
        self.y = y
    
    def __add__(self, b):
        return Sum(self, b)
    
class Sum(Two):
    
    def __init__(self, a, b):
        self.a = a
        self.b = b
    
    @property
    def x(self):
        return self.a.x + self.b.x

    @property
    def y(self):
        return self.a.y + self.b.y