- record

+1

This really does match well with the record concept in databases, and most people are familiar with that. Though it will. E a touch confusing until (if ever) most of the database and cab traders, etc start using them.

It also matches pretty well with numpy "record arrays":

https://docs.scipy.org/doc/numpy-1.13.0/user/basics.rec.html

- bag

I also like this -- not many folks will have a ore-conceived notion of what it is.

- declarative

Yeach-- that's an adjective (at least on most common use) -- and a programming term that means something else.

Also, considering their uses, it might make sense to put them in the collections module.

Yup.

-CHB