>>> from collections import OrderedDict
>>> class Foo(type(OrderedDict({'foo': 'bar'}).keys())): ...
...
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: type 'odict_keys' is not an acceptable base type

The C implementation that's actually used for OrderedDict.keys() at runtime differs from the pure-Python implementation that's exposed as collections._OrderedDictKeysView. This has come up before; it might be good to add a comment about it to the stub. Or alternatively, maybe we should change OrderedDict so that .keys() doesn't return _OrderedDictKeysView, but returns odict_keys or something. But that seems a bit weird, especially since this is the only way I know of in which the pure-Python implementations and the C implementations of these classes differ.

Right now our stubtest does not check @final declaration on regular types. Maybe we should?

This was considered in python/mypy#12091, but rejected due to zero true positives and several false-positives (with the collections hits being considered as false-positives): python/mypy#12091 (comment).