pythongh-144175: Add PyArg_ParseVector() function

Author: vstinner

Doc/c-api/arg.rst

@@ -516,6 +516,17 @@ API Functions
        }
 
 
+.. c:function:: int PyArg_ParseVector(PyObject *const *args, Py_ssize_t nargs, const char *format, ...)
+
+   Parse the parameters of a function that takes only vector parameters into
+   local variables; function using the :c:macro:`METH_FASTCALL` calling
+   convention.
+   Returns true on success; on failure, it returns false and raises the
+   appropriate exception.
+
+   .. versionadded:: 3.15
+
+
 .. c:function:: int PyArg_UnpackTuple(PyObject *args, const char *name, Py_ssize_t min, Py_ssize_t max, ...)
 
    A simpler form of parameter retrieval which does not use a format string to

Doc/whatsnew/3.15.rst

@@ -1255,6 +1255,10 @@ C API changes
 New features
 ------------
 
+* Add :c:func:`PyArg_ParseVector` function to parse arguments of functions
+  using the :c:macro:`METH_FASTCALL` calling convention.
+  (Contributed by Victor Stinner in :gh:`144175`.)
+
 * Add :c:func:`PySys_GetAttr`, :c:func:`PySys_GetAttrString`,
   :c:func:`PySys_GetOptionalAttr`, and :c:func:`PySys_GetOptionalAttrString`
   functions as replacements for :c:func:`PySys_GetObject`.

Include/cpython/modsupport.h

@@ -2,6 +2,12 @@
 #  error "this header file must not be included directly"
 #endif
 
+PyAPI_FUNC(int) PyArg_ParseVector(
+    PyObject *const *args,
+    Py_ssize_t nargs,
+    const char *format,
+    ...);
+
 // A data structure that can be used to run initialization code once in a
 // thread-safe manner. The C++11 equivalent is std::call_once.
 typedef struct {

Misc/NEWS.d/next/C_API/2026-01-27-18-15-15.gh-issue-144175.qHK5Jf.rst

@@ -0,0 +1,3 @@
+Add :c:func:`PyArg_ParseVector` function to parse arguments of functions
+using the :c:macro:`METH_FASTCALL` calling convention. Patch by Victor
+Stinner.

Python/getargs.c

@@ -129,6 +129,16 @@ _PyArg_ParseStack(PyObject *const *args, Py_ssize_t nargs, const char *format, .
     return retval;
 }
 
+int
+PyArg_ParseVector(PyObject *const *args, Py_ssize_t nargs, const char *format, ...)
+{
+    va_list va;
+    va_start(va, format);
+    int retval = vgetargs1_impl(NULL, args, nargs, format, &va, 0);
+    va_end(va);
+    return retval;
+}
+
 int
 PyArg_VaParse(PyObject *args, const char *format, va_list va)
 {