Thank you Stefano and Jonathan for a very carefully written and thought-out PEP. I trust that the background etc. are representing past discussion, so I am going to focus on the spec itself. Fortunately I only have a few nits, really. (If you submit new PRs to the peps repo, one of the PEP editors will merge it quickly without questions, as long as the markup passes the tests.)

- I recommend that you carefully look over the PEP as rendered on python.org (link above) and try to fix any markup oddities. E.g. some comments are line-wrapped, which looks ugly, and some bulleted lists have an extra blank line above.

- Looking at the generated ToC, you have two top-level sections labeled "Syntax and Semantics". That seems a bit odd. I'm not sure what you meant to happen here, but I recommend renaming at least one of these. (Another recommendation: don't mix description of the status quo with the specification.)

- While I can understand the desire to keep C function names short, I don't see we should continue the tradition of using the meaningless 'Ex' suffix for API variations that take an additional dict of keywords. Looking through the existing APIs, I recommend PyObject_{Get,Set,Del}ItemWithKeywords instead. (Note you have a typo here, "DetItem". Also I recommend adding markup (e.g. bullets) so each signature is on a line by itself.

That's it from me!