Question

I’m just getting started with Python, and am trying to figure out the Right Way to use classes.

My program currently has two classes, call them Planner and Model. The Planner is model-agnostic, given that any Model it uses presents a consistent interface. So, it seems like if I want to have several different available models, they should all inherit from something, in order to enforce the consistent interface. Additionally, some of the Model classes will share functionality. For example, a singleAgent Model might simulate one agent, while a doubleAgent Model would simulate two agents, each behaving just like the singleAgent.

So – how should I implement this / what language features do I need?

EDIT: Thanks for the fast responses straightening me out about duck classes! So, it sounds like I would only use inheritance if I wanted to override a subset of another Model‘s functionality? (And for my doubleAgent, I’d probably just use singleAgents as class members?)

_{I’ve taken a look through a few other questions with similar tags, but they seem to be more concerned with syntax rather than design choices. I’ve also looked at the official Python documentation on classes and not found what I’m looking for. (Possibly because I don’t know enough to recognize it.)}

Answer 1

In Python you don’t generally use quite the same approaches to OOP as in statically typed languages. Specifically you don’t actually need an object to implement a specific interface or derive from an abstract base class and so on. Rather that object just needs to be able to do the required operations. This is colloquially known as duck typing. If it walks like a duck and talks like a duck then, to all intents and purposes it is a duck.

So just decide what methods are required for your objects and make sure that they always have them. Should you wish to share implementation between different actors in your system then you can consider class inheritance. But if not then you may as well implement disjoint class hierarchies.