> I think that adding macros makes readability worse.

See the attached PRs, I can remove multiple layers of parenthesis in macros by using CAST macros.

> ```
> PyObject *func = ...;
> int flags = PyCFunction_GET_FLAGS(func);
> ```
>
> is dangerous.

Right.

PEP 670 proposes to remove the cast, but only in the limited C API version 3.11 or newer. Sadly, I don't think that we can remove the cast in the general Python C API, it would simply add too many compiler warnings in existing C extensions which previously built without warnings. (See also PEP 670 discussions on python-dev).

Currently, PyCFunction_GET_FLAGS() doesn't check its argument. The macro documentation is quite explicit about it:

/* Macros for direct access to these values. Type checks are *not*
   done, so use with care. */

My GH-32190 PR adds a check in debug mode. So using PyCFunction_GET_FLAGS() in debug mode is safer with this PR.