gh-129367: Add PySys_GetAttr() function

Author: vstinner

Doc/c-api/sys.rst

@@ -258,6 +258,13 @@ These are utility functions that make functionality from the :mod:`sys` module
 accessible to C code.  They all work with the current interpreter thread's
 :mod:`sys` module's dict, which is contained in the internal thread state structure.
 
+.. c:function:: PyObject *PySys_GetAttr(const char *name)
+
+   Return the object *name* from the :mod:`sys` module.
+
+   Return a new object on success. Set an exception and return ``NULL`` on
+   error.
+
 .. c:function:: PyObject *PySys_GetObject(const char *name)
 
    Return the object *name* from the :mod:`sys` module or ``NULL`` if it does

Doc/data/refcounts.dat

@@ -3052,3 +3052,6 @@ _Py_c_quot:Py_complex:divisor::
 _Py_c_sum:Py_complex:::
 _Py_c_sum:Py_complex:left::
 _Py_c_sum:Py_complex:right::
+
+PySys_GetAttr:PyObject*::+1:
+PySys_GetAttr:const char*:name::

Doc/whatsnew/3.14.rst

@@ -1330,6 +1330,11 @@ New features
   bit-packing Python version numbers.
   (Contributed by Petr Viktorin in :gh:`128629`.)
 
+* Add :c:func:`PySys_GetAttr` function to get an attribute of the :mod:`sys`
+  module. Compared to :c:func:`PySys_GetObject`, it doesn't ignore errors and
+  it returns a :term:`strong reference`.
+  (Contributed by Victor Stinner in :gh:`129367`.)
+
 
 Porting to Python 3.14
 ----------------------

Include/cpython/sysmodule.h

@@ -0,0 +1,5 @@
+#ifndef Py_CPYTHON_SYS_H
+#  error "this header file must not be included directly"
+#endif
+
+PyAPI_FUNC(PyObject *) PySys_GetAttr(const char *);

Include/sysmodule.h

@@ -21,6 +21,12 @@ Py_DEPRECATED(3.13) PyAPI_FUNC(void) PySys_ResetWarnOptions(void);
 
 PyAPI_FUNC(PyObject *) PySys_GetXOptions(void);
 
+#ifndef Py_LIMITED_API
+#  define Py_CPYTHON_SYS_H
+#  include "cpython/sysmodule.h"
+#  undef Py_CPYTHON_SYS_H
+#endif
+
 #ifdef __cplusplus
 }
 #endif

Lib/test/test_capi/test_sys.py

@@ -4,13 +4,12 @@
 from test import support
 from test.support import import_helper
 
-try:
-    import _testlimitedcapi
-except ImportError:
-    _testlimitedcapi = None
+_testlimitedcapi = import_helper.import_module('_testlimitedcapi')
+_testcapi = import_helper.import_module('_testcapi')
 
 NULL = None
 
+
 class CAPITest(unittest.TestCase):
     # TODO: Test the following functions:
     #
@@ -20,7 +19,6 @@ class CAPITest(unittest.TestCase):
     maxDiff = None
 
     @support.cpython_only
-    @unittest.skipIf(_testlimitedcapi is None, 'need _testlimitedcapi module')
     def test_sys_getobject(self):
         # Test PySys_GetObject()
         getobject = _testlimitedcapi.sys_getobject
@@ -37,8 +35,22 @@ def test_sys_getobject(self):
                              "'utf-8' codec can't decode")
         # CRASHES getobject(NULL)
 
+    def test_sys_getattr(self):
+        # Test PySys_GetAttr()
+        sys_getattr = _testcapi.PySys_GetAttr
+
+        self.assertIs(sys_getattr('stdout'), sys.stdout)
+        with support.swap_attr(sys, '\U0001f40d', 42):
+            self.assertEqual(sys_getattr('\U0001f40d'.encode()), 42)
+
+        with self.assertRaises(AttributeError):
+            sys_getattr(b'nonexisting')
+        with self.assertRaises(UnicodeDecodeError):
+            self.assertIs(sys_getattr(b'\xff'), AttributeError)
+
+        # CRASHES sys_getattr(NULL)
+
     @support.cpython_only
-    @unittest.skipIf(_testlimitedcapi is None, 'need _testlimitedcapi module')
     def test_sys_setobject(self):
         # Test PySys_SetObject()
         setobject = _testlimitedcapi.sys_setobject
@@ -70,7 +82,6 @@ def test_sys_setobject(self):
         # CRASHES setobject(NULL, value)
 
     @support.cpython_only
-    @unittest.skipIf(_testlimitedcapi is None, 'need _testlimitedcapi module')
     def test_sys_getxoptions(self):
         # Test PySys_GetXOptions()
         getxoptions = _testlimitedcapi.sys_getxoptions

Misc/NEWS.d/next/C_API/2025-01-27-17-40-20.gh-issue-129367.sm8DvA.rst

@@ -0,0 +1,3 @@
+Add :c:func:`PySys_GetAttr` function to get an attribute of the :mod:`sys`
+module. Compared to :c:func:`PySys_GetObject`, it doesn't ignore errors and
+it returns a :term:`strong reference`. Patch by Victor Stinner.

Modules/Setup.stdlib.in

@@ -162,7 +162,7 @@
 @MODULE__XXTESTFUZZ_TRUE@_xxtestfuzz _xxtestfuzz/_xxtestfuzz.c _xxtestfuzz/fuzzer.c
 @MODULE__TESTBUFFER_TRUE@_testbuffer _testbuffer.c
 @MODULE__TESTINTERNALCAPI_TRUE@_testinternalcapi _testinternalcapi.c _testinternalcapi/test_lock.c _testinternalcapi/pytime.c _testinternalcapi/set.c _testinternalcapi/test_critical_sections.c
-@MODULE__TESTCAPI_TRUE@_testcapi _testcapimodule.c _testcapi/vectorcall.c _testcapi/heaptype.c _testcapi/abstract.c _testcapi/unicode.c _testcapi/dict.c _testcapi/set.c _testcapi/list.c _testcapi/tuple.c _testcapi/getargs.c _testcapi/datetime.c _testcapi/docstring.c _testcapi/mem.c _testcapi/watchers.c _testcapi/long.c _testcapi/float.c _testcapi/complex.c _testcapi/numbers.c _testcapi/structmember.c _testcapi/exceptions.c _testcapi/code.c _testcapi/buffer.c _testcapi/pyatomic.c _testcapi/run.c _testcapi/file.c _testcapi/codec.c _testcapi/immortal.c _testcapi/gc.c _testcapi/hash.c _testcapi/time.c _testcapi/bytes.c _testcapi/object.c _testcapi/monitoring.c  _testcapi/config.c
+@MODULE__TESTCAPI_TRUE@_testcapi _testcapimodule.c _testcapi/vectorcall.c _testcapi/heaptype.c _testcapi/abstract.c _testcapi/unicode.c _testcapi/dict.c _testcapi/set.c _testcapi/list.c _testcapi/tuple.c _testcapi/getargs.c _testcapi/datetime.c _testcapi/docstring.c _testcapi/mem.c _testcapi/watchers.c _testcapi/long.c _testcapi/float.c _testcapi/complex.c _testcapi/numbers.c _testcapi/structmember.c _testcapi/exceptions.c _testcapi/code.c _testcapi/buffer.c _testcapi/pyatomic.c _testcapi/run.c _testcapi/file.c _testcapi/codec.c _testcapi/immortal.c _testcapi/gc.c _testcapi/hash.c _testcapi/time.c _testcapi/bytes.c _testcapi/object.c _testcapi/monitoring.c _testcapi/config.c _testcapi/sys.c
 @MODULE__TESTLIMITEDCAPI_TRUE@_testlimitedcapi _testlimitedcapi.c _testlimitedcapi/abstract.c _testlimitedcapi/bytearray.c _testlimitedcapi/bytes.c _testlimitedcapi/codec.c _testlimitedcapi/complex.c _testlimitedcapi/dict.c _testlimitedcapi/eval.c _testlimitedcapi/float.c _testlimitedcapi/heaptype_relative.c _testlimitedcapi/import.c _testlimitedcapi/list.c _testlimitedcapi/long.c _testlimitedcapi/object.c _testlimitedcapi/pyos.c _testlimitedcapi/set.c _testlimitedcapi/sys.c _testlimitedcapi/tuple.c _testlimitedcapi/unicode.c _testlimitedcapi/vectorcall_limited.c _testlimitedcapi/version.c
 @MODULE__TESTCLINIC_TRUE@_testclinic _testclinic.c
 @MODULE__TESTCLINIC_LIMITED_TRUE@_testclinic_limited _testclinic_limited.c

Modules/_testcapi/parts.h

@@ -61,5 +61,6 @@ int _PyTestCapi_Init_Time(PyObject *module);
 int _PyTestCapi_Init_Monitoring(PyObject *module);
 int _PyTestCapi_Init_Object(PyObject *module);
 int _PyTestCapi_Init_Config(PyObject *mod);
+int _PyTestCapi_Init_Sys(PyObject *mod);
 
 #endif // Py_TESTCAPI_PARTS_H

Modules/_testcapi/sys.c

@@ -0,0 +1,27 @@
+#include "parts.h"
+#include "util.h"
+
+
+static PyObject *
+pysys_getattr(PyObject *self, PyObject *arg)
+{
+    const char *name;
+    Py_ssize_t size;
+    if (!PyArg_Parse(arg, "z#", &name, &size)) {
+        return NULL;
+    }
+
+    return PySys_GetAttr(name);
+}
+
+
+static PyMethodDef test_methods[] = {
+    {"PySys_GetAttr", pysys_getattr, METH_O},
+    {NULL},
+};
+
+int
+_PyTestCapi_Init_Sys(PyObject *m)
+{
+    return PyModule_AddFunctions(m, test_methods);
+}