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[Python-Dev] PEP 590: vectorcall without tp_call

On 29/05/2019 15.29, Petr Viktorin wrote:
> On 5/29/19 2:25 PM, Jeroen Demeyer wrote:
>> Hello,
>> I have one implementation question about vectorcall which is not
>> specified in PEP 590: what should happen if a type implements
>> vectorcall (i.e. _Py_TPFLAGS_HAVE_VECTORCALL is set) but doesn't set
>> tp_call (i.e. tp_call == NULL)? I see the following possibilities:
>> 1. Ignore this problem/assume that it won't happen. This would be bad,
>> since callable(obj) would be False even though obj() would succeed.
>> 2. Raise SystemError.
>> 3. Automatically set tp_call to PyVectorcall_Call.
>> I would vote for 3 since it's the most user-friendly option. There is
>> also no way how it could be wrong: it ensures that tp_call and
>> vectorcall are consistent.
> That sounds like a good idea for PyType_FromSpec.
> For static types I either wouldn't bother at all, or only check in debug
> ?builds and fail with Py_FatalError.

You could add a check to PyType_Ready() and have it either return an
error or fix tp_call.