Metaclasses

The class of a class: metaclasses customise how classes themselves are created.

Expert

class Registry(type):
    plugins = {}
    def __new__(mcls, name, bases, ns):
        cls = super().__new__(mcls, name, bases, ns)
        mcls.plugins[name] = cls
        return cls

class Plugin(metaclass=Registry): pass

Most needs are better met by class decorators or __init_subclass__. Frameworks like Django's ORM use metaclasses.

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