bpo-46409: Make generators in bytecode by markshannon · Pull Request #30633 · python/cpython

It is a lie.

We don't want to expose InterpreterFrame in public headers, so we can't do the sensible thing and declare gi_frame as:

    InterpreterFrame gi_frame;

as C won't allow incomplete types in structs, even as the last member.

We could improve this by breaking up the header, so the public API sees a different definition. Still a lie, but a more elegant one.
Public header:

typedef struct {
    _PyGenObject_HEAD(gi)
} PyGenObject;

Private header:

typedef struct {
    _PyGenObject_HEAD(gi)
    InterpreterFrame gi_frame;
} PyGenObject;

Probably best done in a different PR, though.