Comment by mannykannot

I don't think the author is intending to say there is anything wrong in this particular example; he is, rather, anticipating some ways in which this might obfuscate code, either accidentally or deliberately. The rest of the article investigates some of these possibilities and demonstrates that you can, indeed, do so.

Perhaps it would have been a bit clearer, and less easy to dismiss as a fuss over nothing, if the author had left the 'not' out of the definition of NotIterable.__subclasshook__(), or defined an IsIterable class with the 'not' in place?