Use of argument clinic like parsing and METH_FASTCALL support in extension modules #83528

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1. seberg commented on Jan 15, 2020

   

   sebergmannequin

   on Jan 15, 2020

   MannequinAuthor

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   This is mainly an information request, so sorry if its a bit besides the point (I do not mind if you just close it). But it seemed a bit too specific to get answers in most places...
   In Python you use argument clinic, which supports METH_FASTCALL, that seems pretty awesome.

   For extension modules, I am not sure that argument clinic is a straight forward choice, since it probably generates code specific to a single Python version and also using, while we need to support multiple versions (including versions that do not support METH_FASTCALL.

   So the question would be if there is some idea for providing such C-API, or for example exposing _PyArg_UnpackKeywords (which is at the heart of kwarg parsing).

   My use-case is that some NumPy functions do have a nice speedup when using METH_FASTCALL and better argument clinic style faster arg-parsing. Which is why, looking at these things, I practically reimplemented a slightly dumbed down version of PyArg_ParseTupleAndKeywords working much like argument clinic (except less smart and only using macros and no code generation).

   That seems viable, but also feels a bit wrong, so I am curious if there may be a better solution or whether it would be plausible to expose _PyArg_UnpackKeywords to reduce code duplication. (although I suppose due to old python version support that would effectively take years)

   For completeness, my code in question is here: numpy/numpy#15269 with the actual usage pattern being:

   static PyObject *my_method(PyObject *self, NPY_ARGUMENTS_DEF)
   {
       NPY_PREPARE_ARGPARSER;
       PyObject *argument1;
       int argument2 = -1;
       if (!npy_parse_arguments("method", 1, -1, NPY_ARGUMENTS_PASS),
                   "argument1", NULL, &argument1,
                   "argument2", &PyArray_PythonPyIntFromInt, &argument2,
                   NULL, NULL, NULL) {
           return NULL;
       }
   }
2. seberg

   added

   topic-argument-clinic

   type-featureA feature request or enhancementA feature request or enhancement

   on Jan 15, 2020
3. ezio-melotti

   transferred this issue fromon Apr 10, 2022