Hey Ivan,

There seem to be some action items from this thread that I haven't seen reflected in the PEP source code yet.
- Change the title (I like "Core support for typing module and generic types" but maybe it can be shortened to "Core support for generics in the typing module" -- if you like that, go for it)
- Change __subclass_base__ to __mro_entry__
- Add
types.resolve_bases and related changes
- Maybe some clarifications summarizing the feedback from this thread (esp. Nick's)?

Then the next step I propose is a PR with a full implementation. After that I'll likely approve the PEP (or we'll have minor feedback based on trying the implementation).

I don't require a new typing.py that uses these features to be part of the "full implementation" but it would be nice to make a start with that as well -- if we can make the case that it will speed up "import typing" a lot then that would be a powerful argument for the PEP.

--Guido van Rossum (python.org/~guido)