How do I properly override __setattr__ and __getattribute__ on new-style classes in Python?

It’s

super(ABCImmutable, self).__setattr__(name, value)

in Python 2, or

super().__setattr__(name, value)

in Python 3.

Also, raising AttributeError is not how you fall back to the default behavior for __getattribute__. You fall back to the default with

return super(ABCImmutable, self).__getattribute__(name)

on Python 2 or

return super().__getattribute__(name)

on Python 3.

Raising AttributeError skips the default handling and goes to __getattr__, or just produces an AttributeError in the calling code if there’s no __getattr__.

See the documentation on Customizing Attribute Access.