Namedtuples FTW! A de-facto immutable dict with the keys listed right there in the definition to obviate all the usage head-scratching. Then, if you need more functionality (eg factory functions to fill in sensible defaults), you can just subclass it.

TBH I've never understood the attraction of the untyped dict beyond simple one-off hackups (and even there namedtuples are preferable), because like you say you typically have no idea what's supposed to be in there.