Metaclasses / __init_subclass__ are generally only used if you try to define different / new behavior for how the body of a class is interpreted. So if you'd wa

Metaclasses / __init_subclass__ are generally only used if you try to define different / new behavior for how the body of a class is interpreted. So if you'd want to create e.g. an explicit interface system in Python, you might use them. If you're creating an ORM or some other kind of declarative property system, you might use them (but not necessarily, as descriptors are a thing). I think the only use in the standard library is in ABCs and probably the typing module. Edit: Enums use them as well (makes sense).