It's quite arguably a bugfix, since datetime.h in 2.3.4 exposes things that can't possibly be used outside of datetimemodule.c (the datetime type objects are referenced in the header, but not exported in a usable way). Anthony Tuininga's patch to *finish* (not really add) the datetime C API is a low-risk change regardless: it doesn't change any existing functionality, it just finishes the job of exposing it to C coders, and adds some new macros for convenience.
Now if some platform header file has macros with names like
PyDateTime_FromTimestamp or PyDelta_FromDSU
then adding these macros to datetime.h could cause new problems. But platform header files don't have macros with names like those (if they did, we would have bumped into it while developing 2.4).
Hm, Anthony, what do you think now? (Disregard my previous mail, I was confused by multiple logical threads mixed into the same conversation.) --Guido