Newer versions of Python have an in-band way of detecting if an object has been overridden. Foreseeably this could have been done completely internal to the VM.

Newer versions of Python have an in-band way of detecting if an object has been overridden. Foreseeably this could have been done completely internal to the VM. Defaulting to closed and requiring an explicit step to override behavior would have made optimizing Python far easier.