gh-129367: Add PySys_GetAttr() function

Doc/c-api/sys.rst

@@ -258,6 +258,24 @@ 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(PyObject *name)
+
+   Return the object *name* from the :mod:`sys` module.
+
+   Return a new object on success. Set an exception and return ``NULL`` on
+   error.
+
+   .. versionadded:: next
+
+
+.. c:function:: PyObject *PySys_GetAttrString(const char *name)
+
+   Similar to :c:func:`PySys_GetAttr`, but *name* is an UTF-8 encoded
+   string.
+
+   .. versionadded:: next
+
+
 .. 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 +3052,9 @@ _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:PyObject*:name:0:
+
+PySys_GetAttrString:PyObject*::+1:
+PySys_GetAttrString:const char*:name::

Doc/whatsnew/3.14.rst

@@ -1322,6 +1322,12 @@ New features
 * Add :c:func:`PyUnstable_IsImmortal` for determining whether an object is :term:`immortal`,
   for debugging purposes.
 
+* Add :c:func:`PySys_GetAttr` and :c:func:`PySys_GetAttrString` functions to
+  get an attribute of the :mod:`sys` module. Compared to
+  :c:func:`PySys_GetObject`, they don't ignore errors and return a
+  :term:`strong reference`.
+  (Contributed by Victor Stinner in :gh:`129367`.)
+
 
 Limited C API changes
 ---------------------

Include/cpython/sysmodule.h

@@ -0,0 +1,6 @@
+#ifndef Py_CPYTHON_SYS_H
+#  error "this header file must not be included directly"
+#endif
+
+PyAPI_FUNC(PyObject *) PySys_GetAttr(PyObject *name);
+PyAPI_FUNC(PyObject *) PySys_GetAttrString(const char *name);

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:
     #
@@ -19,15 +18,18 @@ class CAPITest(unittest.TestCase):
 
     maxDiff = None
 
+    def check_sys_getattr_common(self, sys_getattr):
+        self.assertIs(sys_getattr('stdout'), sys.stdout)
+
+        with support.swap_attr(sys, '\U0001f40d', 42):
+            self.assertEqual(sys_getattr('\U0001f40d'), 42)
+
     @support.cpython_only
-    @unittest.skipIf(_testlimitedcapi is None, 'need _testlimitedcapi module')
     def test_sys_getobject(self):
         # Test PySys_GetObject()
         getobject = _testlimitedcapi.sys_getobject
 
-        self.assertIs(getobject(b'stdout'), sys.stdout)
-        with support.swap_attr(sys, '\U0001f40d', 42):
-            self.assertEqual(getobject('\U0001f40d'.encode()), 42)
+        self.check_sys_getattr_common(getobject)
 
         self.assertIs(getobject(b'nonexisting'), AttributeError)
         with support.catch_unraisable_exception() as cm:
@@ -37,8 +39,37 @@ def test_sys_getobject(self):
                              "'utf-8' codec can't decode")
         # CRASHES getobject(NULL)
 
+    def check_sys_getattr(self, sys_getattr):
+        self.check_sys_getattr_common(sys_getattr)
+
+        with self.assertRaises(AttributeError):
+            sys_getattr(b'nonexisting')
+
+    def test_sys_getattr(self):
+        # Test PySys_GetAttr()
+        sys_getattr = _testcapi.PySys_GetAttr
+
+        self.check_sys_getattr(sys_getattr)
+
+        with self.assertRaises(TypeError):
+            for invalid_name in (123, [], object()):
+                with self.assertRaises(AttributeError):
+                    sys_getattr(invalid_name)
+
+        # CRASHES sys_getattr(NULL)
+
+    def test_sys_getattrstring(self):
+        # Test PySys_GetAttr()
+        sys_getattrstring = _testcapi.PySys_GetAttrString
+
+        self.check_sys_getattr(sys_getattrstring)
+
+        with self.assertRaises(UnicodeDecodeError):
+            self.assertIs(sys_getattrstring(b'\xff'), AttributeError)
+
+        # CRASHES sys_getattrstring(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 +101,6 @@ 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 +1,4 @@
+Add :c:func:`PySys_GetAttr` and :c:func:`PySys_GetAttrString` functions to get
+an attribute of the :mod:`sys` module. Compared to :c:func:`PySys_GetObject`,
+they don't ignore errors and return 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 +1,36 @@
+#include "parts.h"
+#include "util.h"
+
+
+static PyObject *
+pysys_getattr(PyObject *self, PyObject *name)
+{
+    NULLABLE(name);
+    return PySys_GetAttr(name);
+}
+
+
+static PyObject *
+pysys_getattrstring(PyObject *self, PyObject *arg)
+{
+    const char *name;
+    Py_ssize_t size;
+    if (!PyArg_Parse(arg, "z#", &name, &size)) {
+        return NULL;
+    }
+
+    return PySys_GetAttrString(name);
+}
+
+
+static PyMethodDef test_methods[] = {
+    {"PySys_GetAttr", pysys_getattr, METH_O},
+    {"PySys_GetAttrString", pysys_getattrstring, METH_O},
+    {NULL},
+};
+
+int
+_PyTestCapi_Init_Sys(PyObject *m)
+{
+    return PyModule_AddFunctions(m, test_methods);
+}

Modules/_testcapimodule.c

@@ -4401,6 +4401,9 @@ PyInit__testcapi(void)
     if (_PyTestCapi_Init_Config(m) < 0) {
         return NULL;
     }
+    if (_PyTestCapi_Init_Sys(m) < 0) {
+        return NULL;
+    }
 
     PyState_AddModule(m, &_testcapimodule);
     return m;

PCbuild/_testcapi.vcxproj

@@ -127,6 +127,7 @@
     <ClCompile Include="..\Modules\_testcapi\run.c" />
     <ClCompile Include="..\Modules\_testcapi\monitoring.c" />
     <ClCompile Include="..\Modules\_testcapi\config.c" />
+    <ClCompile Include="..\Modules\_testcapi\sys.c" />
   </ItemGroup>
   <ItemGroup>
     <ResourceCompile Include="..\PC\python_nt.rc" />

PCbuild/_testcapi.vcxproj.filters

@@ -114,6 +114,9 @@
     <ClCompile Include="..\Modules\_testcapi\config.c">
       <Filter>Source Files</Filter>
     </ClCompile>
+    <ClCompile Include="..\Modules\_testcapi\sys.c">
+      <Filter>Source Files</Filter>
+    </ClCompile>
   </ItemGroup>
   <ItemGroup>
     <ResourceCompile Include="..\PC\python_nt.rc">

Python/sysmodule.c

@@ -86,6 +86,42 @@ _PySys_GetAttr(PyThreadState *tstate, PyObject *name)
     return value;
 }
 
+
+PyObject*
+PySys_GetAttr(PyObject *name)
+{
+    PyInterpreterState *interp = _PyInterpreterState_GET();
+    PyObject *sys_dict = interp->sysdict;
+    if (sys_dict == NULL) {
+        PyErr_SetString(PyExc_RuntimeError, "lost sys module");
+        return NULL;
+    }
+    PyObject *value;
+    if (PyDict_GetItemRef(sys_dict, name, &value) < 0) {
+        return NULL;
+    }
+    if (value == NULL) {
+        PyErr_Format(PyExc_AttributeError, "sys has no attribute %s", name);
+        return NULL;
+    }
+    return value;
+}
+
+
+PyObject*
+PySys_GetAttrString(const char *name)
+{
+    PyObject *name_obj = PyUnicode_FromString(name);
+    if (name_obj == NULL) {
+        return NULL;
+    }
+
+    PyObject *value = PySys_GetAttr(name_obj);
+    Py_DECREF(name_obj);
+    return value;
+}
+
+
 static PyObject *
 _PySys_GetObject(PyInterpreterState *interp, const char *name)
 {
@@ -3150,11 +3186,8 @@ sys_set_flag(PyObject *flags, Py_ssize_t pos, PyObject *value)
 int
 _PySys_SetFlagObj(Py_ssize_t pos, PyObject *value)
 {
-    PyObject *flags = Py_XNewRef(PySys_GetObject("flags"));
+    PyObject *flags = PySys_GetAttrString("flags");
     if (flags == NULL) {
-        if (!PyErr_Occurred()) {
-            PyErr_SetString(PyExc_RuntimeError, "lost sys.flags");
-        }
         return -1;
     }
 
@@ -3713,16 +3746,15 @@ _PySys_UpdateConfig(PyThreadState *tstate)
 #undef COPY_WSTR
 
     // sys.flags
-    PyObject *flags = _PySys_GetObject(interp, "flags"); // borrowed ref
+    PyObject *flags = PySys_GetAttrString("flags");
     if (flags == NULL) {
-        if (!_PyErr_Occurred(tstate)) {
-            _PyErr_SetString(tstate, PyExc_RuntimeError, "lost sys.flags");
-        }
         return -1;
     }
     if (set_flags_from_config(interp, flags) < 0) {
+        Py_DECREF(flags);
         return -1;
     }
+    Py_DECREF(flags);
 
     SET_SYS("dont_write_bytecode", PyBool_FromLong(!config->write_bytecode));