> Instead, every call must go through PyObject_CallMethod, and the file
> objects only handle `PyBytes` and `PyByteArray` which are cumbersome
> and inefficient to use in extension modules.

Because of the generic nature of the 3.x I/O stack, even shortcuts such as the proposed PyFile_Write will still have to use PyObject_CallMethod(obj, "write", ...) under the hood.

As for the types handled by file objects, you should be able to use a PyMemoryViewObject, which allows you to create a memory buffer without copying it (if that's what you're after).
You can also pass your own objects provided they support the new buffer API: http://docs.python.org/dev/c-api/buffer.html#bufferobjects
(I agree this documentation is not very well written, though)

So, bottom line, we could create a set of PyFile_* wrappers (or, rather, PyStream_*), but they wouldn't be much more efficient that what you can write by hand. Do you still think it's worth it? If so, I think you should float the idea on python-dev (the mailing-list).