Include/internal/pycore_modsupport.h

Source:

cpython 3.14 @ ab2d84fe1023/Include/internal/pycore_modsupport.h ↗

pycore_modsupport.h declares internal variants of the argument-parsing and value-building APIs used by the CPython clinic-generated code.

Map

Lines	Symbol	Role
1-40	_PyArg_ParseStack	Parse args from a C array without building a tuple
41-70	_PyArg_NoKeywords	Raise TypeError if kwargs dict is non-empty
71-90	_PyArg_NoPositional	Raise TypeError if positional args are present
91-120	_Py_VaBuildValue	Internal Py_BuildValue using a va_list

Reading

_PyArg_ParseStack

// CPython: Include/internal/pycore_modsupport.h:18 _PyArg_ParseStack
/* Like PyArg_ParseTuple but takes the raw C argument array instead of a tuple.
   Used by METH_FASTCALL methods to avoid constructing a PyTupleObject. */
int _PyArg_ParseStack(PyObject *const *args, Py_ssize_t nargs,
                      const char *format, ...);

METH_FASTCALL passes arguments as PyObject **args, Py_ssize_t nargs rather than a PyTupleObject. _PyArg_ParseStack parses this array directly, avoiding the PyTuple_New overhead.

_PyArg_NoKeywords

// CPython: Include/internal/pycore_modsupport.h:44 _PyArg_NoKeywords
/* Raise TypeError("funcname() takes no keyword arguments") if kwargs != NULL.
   Called by METH_FASTCALL|METH_KEYWORDS methods that don't accept kwargs. */
int _PyArg_NoKeywords(const char *funcname, PyObject *kwargs);

_PyArg_CheckPositional

// CPython: Include/internal/pycore_modsupport.h:60 _PyArg_CheckPositional
/* Validate that nargs is within [min, max].
   If not, raise TypeError with a helpful message. */
int _PyArg_CheckPositional(const char *name,
                            Py_ssize_t nargs,
                            Py_ssize_t min, Py_ssize_t max);

_Py_VaBuildValue

// CPython: Include/internal/pycore_modsupport.h:100 _Py_VaBuildValue
/* Internal variant of Py_BuildValue that takes a va_list.
   Used by clinic-generated code and by PyObject_CallFunction. */
PyObject * _Py_VaBuildValue(const char *format, va_list va);

Py_BuildValue("(ii)", x, y) calls _Py_VaBuildValue internally to construct (x, y) as a Python tuple.

Clinic-generated usage pattern

/* Argparse clinic generates code like:
   static PyObject *
   os_open_impl(PyObject *module, path_t *path, int flags, int mode, ...)
   {
       ...
   }

   static PyObject *
   os_open(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
   {
       ...
       if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames,
           &_parser, &path, &flags, &mode, ...))
           return NULL;
       return os_open_impl(module, &path, flags, mode, ...);
   }
*/

gopy notes

gopy's argument parsing uses vm.ParseArgs / vm.ParseArgsKwargs in vm/argparse.go. _PyArg_NoKeywords maps to vm.NoKeywords. _Py_VaBuildValue has no direct equivalent; gopy constructs tuples using objects.NewTuple(items...). Clinic-generated METH_FASTCALL methods pass []*PyObject slices directly.