"tp_print" has been marked as reserved for all of Python 3. To me, that means deprecated and do not use. (But perhaps that ought to have been properly defined in the docs?)

Cython should not be using this field directly. If all they're doing is setting it to NULL, they can equally easily zero out the entire structure and ignore it without changing behavior on any Python 3.x.

I have no problem changing the names of deprecated/reserved fields in PyTypeObject between releases. Source compatibility guarantees do not extend that far.