> Why the concrete str type for strings, but not for lists Because you would need to extend the base list type to support indexing just for this feature, which

> Why the concrete str type for strings, but not for lists Because you would need to extend the base list type to support indexing just for this feature, which is a bit iffy if you ask me. I think you have a point about "don't check against concrete types" though, they should update the docs to suggest using an 'Iterable[type]' over a 'List[type]' unless you really really really want a list.