Behaving differently on an empty list than on no list is a huge smell. That's really weird and unexpected behavior. Doing it for testing is even weirder. If yo

Behaving differently on an empty list than on no list is a huge smell. That's really weird and unexpected behavior. Doing it for testing is even weirder. If you're fetching an element from a dictionary and want not-present to be the same as some false value, fetch with a default value (in Python, pass a second parameter to get()) that you want to see when there's nothing present. Or just extract the value and check for nil or empty separately, nothing wrong with being explicit.