I uploaded the patch just before your comment Nick.

Here is updated patch. Functions are renamed as Nick suggested, added two more functions: decompose_astrals() and compose_surrogate_pairs(). They are mainly for example here, they can be committed in other issue.

I hesitate about the rehandle_surrogatepass name. This function handles surrogates than can be created not only with the "surrogatepass" handler, but also with different ways, e.g. with the "surrogateescape" handler, with chr(), handle_astral() or decompose_astrals(). Actually it checks that the string is valid Unicode (not containing surrogates) and handle errors if found with specified error handler.

May be there is a time for wider discussion on Python-Dev. I especially want to hear opinions of Ezio and Martin.