One possible downside to the `classattribute` route is that we have a descriptor whose only purpose is to shield the item from becoming a member; the up-side is that it's simple to implement.

Another possibility is `skip`:

class skip:
    """
    Protects item from becaming an Enum member during class creation.
    """
    def __init__(self, value):
        self.value = value

    def __get__(self, instance, ownerclass=None):
        return self.value

The advantage is that it is replaced by the metaclass with the stored value, so we have no extraneous descriptor after the Enum is created; the downside is that it requires change in the metaclass to do the right thing.

Thoughts?