We have:

    # Concrete collection types.
    'Dict',
    'DefaultDict',
    'List',
    'Set',
    'FrozenSet',
    'NamedTuple',  # Not really a type.
    'Generator',

But no mention of Deque.

What this an intended omission?

I would like to be able to write something like this:

   user_posts = defaultdict(deque)  # type: DefaultDict[User, Deque[Post]]