I'm sure this has a simple explanation (and is probably only of
historical interest at this point), but ...
While starting to port the Python Sybase module to Python 3, among other
hurdles, I noticed that RO is no longer defined. Looking in
structmember.h, I see that most of the macros defined there are missing
a PY_ prefix. Given that these are macros which are likely to be used by
extension modules and are thus really part of the C API, shouldn't they
have PY_ or _PY_ prefixes? This file got its start in 1990, so would
surely have been around for the great renaming
<http://python-history.blogspot.com/2009/03/great-or-grand-renaming.html>.
Looking at the documentation on defining new types, I saw no mention of
these peculiarly named constants, though they are clearly documented.