How to auto register a class when it's defined

Question

I want to have an instance of class registered when the class is defined. Ideally the code below would do the trick.

registry = {}

def register( cls ):
            


        

Answer 1

Since python 3.6 you don't need metaclasses to solve this

In python 3.6 simpler customization of class creation was introduced (PEP 487).

An __init_subclass__ hook that initializes all subclasses of a given class.

Proposal includes following example of subclass registration

class PluginBase:
    subclasses = []

    def __init_subclass__(cls, **kwargs):
        super().__init_subclass__(**kwargs)
        cls.subclasses.append(cls)

In this example, PluginBase.subclasses will contain a plain list of all subclasses in the entire inheritance tree. One should note that this also works nicely as a mixin class.