[issue37250] C files generated by Cython set tp_print to NULL: PyTypeObject.tp_print removed, replaced with tp_vectorcall_offset

[STINNER Victor]

STINNER Victor <vstinner at redhat.com> added the comment:

me:
> I understand that tp_vectorcall_offset=0 is fine and the expected value for a type which doesn't have the flag _Py_TPFLAGS_HAVE_VECTORCALL.

Jeroen Demeyer:
> Not necessarily. There are subtleties involved when subclassing: there are cases where tp_vectorcall_offset needs to be non-zero despite _Py_TPFLAGS_HAVE_VECTORCALL not being set. See also PR 13858.

Cython generates C code which looks like:

if (PyType_Ready(type) < 0) { ... handle error ... }
type->tp_print = 0;

This code can cause subtle and annoying issue if PR 13858 is merged. So that's another argument in favor of reintroducing tp_print in Python 3.8.

--

Cython has already been fixed to no longer set tp_print to 0 on Python 3.8:

https://github.com/cython/cython/commit/f10a0a391edef10bd37095af87f521808cb362f7

But again, this problem is not about correctness, but more about practical backward compatibility issues (see my first message).

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