OK, thanks for the feedback. I signed the CLA.

I'll then wait with the remaining work, until a final decision has been made. We have a rough idea of how it could be implemented if it comes to this - adding a wrapper function in Python/errors.c:

    PyErr_SetAttributeError(PyObject *attr, const char *format, ...)

that would replace all the PyErr_SetObject, PyErr_SetString and PyErr_Format calls (in around 50 files), create the kwargs object, format the message (if provided) and call PyErr_SetObject or PyErr_SetFormat.

I put the last patch as a commit in the attr bookmark on BitBucket (took me quite some time to figure out that's the alternative to git branches), so that subsequent changes go more easily.