simple example of type specialisation with Python

gistfile1.py

from functools import wraps


def specific_magic(f):
    @wraps(f)
    def wrapper(self, *args, **kwargs):
        for arg in args:
            if type(arg) != self.__class__:
                raise TypeError('{} not of type {}'.format(
                    arg, self.__class__.__name__
                ))

        return f(self, *args, **kwargs)

    return wrapper


class FruitBox(object):
    def __init__(self, num=0):
        self.num = num

    @specific_magic
    def __add__(self, other):
        self.num += other.num
        return self

    def __repr__(self):
        return "{} {}'s".format(self.num, self.__class__.__name__)


class AppleBox(FruitBox):
    pass


class OrangeBox(FruitBox):
    pass