factory example

factory.py

#!/usr/bin/env python3

import abc
from abc import ABCMeta

class FactoryItem(metaclass=ABCMeta):
    def __init__(self, data):
        self.arg1 =  int(data.split()[0])
        self.arg2 =  int(data.split()[2])

    @classmethod
    @abc.abstractmethod
    def wants(cls, data):
        pass

    @abc.abstractmethod
    def awesome_method():
        pass

class Factory():
    classes = []

    @staticmethod
    def register(itemClass):
        Factory.classes.append(itemClass)
        return itemClass

    @staticmethod
    def create(data):
        for cls in Factory.classes:
            if cls.wants(data):
                return cls(data)
        return None

    @staticmethod
    def create_direct(cls, data):
        print(cls)
        return cls(data)

@Factory.register
class MyItem1(FactoryItem):
    @classmethod
    def wants(cls, data):
        return "+" in data

    def awesome_method(self):
        return self.arg1 + self.arg2

@Factory.register
class MyItem2(FactoryItem):
    @classmethod
    def wants(cls, data):
        return "-" in data

    def awesome_method(self):
        return self.arg1 - self.arg2

a = Factory.create("1 + 2")
print(a.awesome_method())

b = Factory.create("1 - 2")
print(b.awesome_method())

c = Factory.create_direct(MyItem1, "1 - 2")
print(c.awesome_method())