gh-116646: Add PyLong_FileDescriptor_Converter() function

Author: vstinner

Doc/c-api/long.rst

@@ -464,3 +464,10 @@ distinguished from a number.  Use :c:func:`PyErr_Occurred` to disambiguate.
 
    Otherwise, the return value is undefined.
 
+.. c:function:: int PyLong_FileDescriptor_Converter(PyObject *p, void *ptr)
+
+   Convert a Python object to a file descript (C ``int`` type).
+   Set `*ptr` and return ``1`` on success. Set an exception and return ``0`` on error.
+
+   It can be used with the ``O&`` format when :ref:`parsing arguments
+   <arg-parsing>`.

Doc/whatsnew/3.13.rst

@@ -1645,6 +1645,10 @@ New Features
   between native integer types and Python :class:`int` objects.
   (Contributed by Steve Dower in :gh:`111140`.)
 
+* Add :c:func:`PyLong_FileDescriptor_Converter` function: convert a Python
+  object to a file descriptor. Function added the limited C API.
+  (Contributed by Victor Stinner in :gh:`116646`.)
+
 
 Porting to Python 3.13
 ----------------------

Include/fileutils.h

@@ -50,6 +50,12 @@ PyAPI_FUNC(char*) Py_EncodeLocale(
     size_t *error_pos);
 #endif
 
+#if !defined(Py_LIMITED_API) || Py_LIMITED_API+0 >= 0x030d0000
+// PyArg converter to convert a Python int objet to a C int.
+// Return 1 on success. Set an exception and return 0 on error.
+PyAPI_FUNC(int) PyLong_FileDescriptor_Converter(PyObject *, void *);
+#endif
+
 #ifndef Py_LIMITED_API
 #  define Py_CPYTHON_FILEUTILS_H
 #  include "cpython/fileutils.h"

Include/internal/pycore_fileutils.h

@@ -312,9 +312,6 @@ extern HRESULT PathCchSkipRoot(const wchar_t *pszPath, const wchar_t **ppszRootE
 #  define _Py_END_SUPPRESS_IPH
 #endif /* _MSC_VER >= 1900 */
 
-// Export for 'select' shared extension (Argument Clinic code)
-PyAPI_FUNC(int) _PyLong_FileDescriptor_Converter(PyObject *, void *);
-
 // Export for test_peg_generator
 PyAPI_FUNC(char*) _Py_UniversalNewlineFgetsWithSize(char *, int, FILE*, PyObject *, size_t*);
 

Misc/NEWS.d/next/C API/2024-03-12-13-56-14.gh-issue-116646.sW27CQ.rst

@@ -0,0 +1,2 @@
+Add PyLong_FileDescriptor_Converter function: convert a Python object to a
+file descriptor. Function added the limited C API. Patch by Victor Stinner.