Python - 迭代扩展类的类列表？

Question

I have a certain class, namely Animal , and several subclasses like Dog , Cow , Lion , etc.

Animal is an abstract class which has an abstract static method eats(Food f) .

All of these subclasses implement eats and, according to each animal, will either return True or False .

How can I iterate through each of those and create a new Animal whose type eats that specific food without manually typing each class?

For example, I'd like to get an object of type Animal that eats grass, without actually creating a new Cow .

Finding the subclasses of Animal may be one part, but I am more interested in actually iterating some sort of list of classes and running eats on each of them, until I find one that returns True and then create a new object of that class.

Thanks.

Answer 1

You could iterate over all subclasses, do the checks and then get the first one which matches:

def create_animal_eating(food):
    gen = (subclass for subclass in Animal.__subclasses__() if subclass.eats(food))
    subclass = next(gen, None)
    if subclass is None:
        raise ValueError("No animal eats " + repr(food))
    new_obj = subclass()

This essentially does exactly what you describe and thus doesn't need any explanation.

But it gets only the immediate subclasses; if you really need all subclasses no matter how deep they are nested, refer to the linked article.