Abstract factory

- Abstract Factory is especially useful when a client expects to receive a family of related objects at a given time, but don't have to know which family it is until run time. Here is the scenario we'll be using. We'll first build a pet factory whose concrete factories include Dog factory and Cat factory. Both dog and cat factories produce related products such as dog food and cat food.

At least in theory our solution, Abstract Factory, consists of Abstract factory, Concrete factory, Abstract product, and Concrete product. For the Abstract factory we use pet factory in our example. For concrete factory we use dog factory and cat factory in our example. And finally for the concrete product we'll be creating the dog, which is a pet, and the dog food, and also cat and the cat food.

We implement our Abstract Factory without using inheritance, mainly because Python is a dynamically typed language and therefore does not require abstract classes. Abstract Factory is related to factory method and the concrete factories are often singletons.