I'd wondered about that with respect to rehandle_surrogatepass.

The current implementation looks like it processes *all* surrogates (even valid surrogate pairs), so "handle_surrogates" might be a suitable name.

If the intent is for it to be "handle_lone_surrogates", I'm not sure the current implementation achieves that, as a valid surrogate pair will match re.compile('[\ud800-\uefff]+').

The rest looks OK to me, including the decompose_astrals() and compose_surrogate_pairs() functions. Regardless of any practical utility, the latter two seem useful for *educational* purposes when it comes to unicode, by making it clear how to switch between the single code point and dual code point representations of the astrals.