@Antoine @Guido:

Some of the possible options for the title are:

* Protocols (structural subtyping)

* Protocols (static duck typing)

* Structural subtyping (static duck typing)

which one do you prefer?

@Nick:

Yes, explicit imports are not necessary for static type checkers (I will add a short comment about this).

@Mark:

I agree with Guido on all points here. For example, collections.abc.Iterable is already a class,
and lots of code uses isinstance(obj, collections.abc.Iterable) and similar checks with other ABCs
(also in a structural manner, i.e. via __subclasshook__). So that disabling this will case many breakages.
The question of whether typing.Iterable[int] should be a class is independent (orthogonal) and
does not belong to this PEP.

--

Ivan