In the Zope 3 book the method is like this:
Looking in some real zope3 tests I saw another version of the method:
NotImplemented is a singleton object, introduced in 2.1 (I think), used
for rich comparision:
I suspect (although I'm often wrong!) the author of the book you are
reading might have used it incorrectly.
NotImplementedError is an exception to raise to indicate that a feature
or method is not implemented. It's probably the one you want.
Zope3-users mailing list