Here is the patch containing unit test only to confirm existing behaviour. So people can learn what to expect when they delete Enum attributes.

Even if we *decide* to change the behaviour of "del MyPet.CUTE_CAT" (assuming CUTE_CAT is an Enum member), I sense that we would only change the exception message not the exception type. That is, it still throws AttributeError but with better error message, such as "Cannot delete attribute."