From 92b1e83c8d8f5f7d1acecf213f97dcf3e8d7a19e Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@python.org>
Date: Sat, 24 Oct 2026 19:07:34 +0100
Subject: [PATCH 1/2] Fix ignored error returns in `sys` initialization,
 `_ctypes` and `_interpchannels`

---
 Modules/_ctypes/_ctypes.c       | 26 +++++++++++++++++---------
 Modules/_interpchannelsmodule.c |  2 +-
 Python/pylifecycle.c            | 20 ++++++++++++++++----
 Python/sysmodule.c              |  8 ++++++--
 4 files changed, 40 insertions(+), 16 deletions(-)

diff --git a/Modules/_ctypes/_ctypes.c b/Modules/_ctypes/_ctypes.c
index a2e5cbab10944b8..1035c91005759df 100644
--- a/Modules/_ctypes/_ctypes.c
+++ b/Modules/_ctypes/_ctypes.c
@@ -2479,22 +2479,30 @@ PyCSimpleType_init(PyObject *self, PyObject *args, PyObject *kwds)
         }
         assert(sw_info);
 #ifdef WORDS_BIGENDIAN
-        PyObject_SetAttrString(self, "__ctype_le__", swapped);
-        PyObject_SetAttrString(self, "__ctype_be__", self);
-        PyObject_SetAttrString(swapped, "__ctype_be__", self);
-        PyObject_SetAttrString(swapped, "__ctype_le__", swapped);
+        if (PyObject_SetAttrString(self, "__ctype_le__", swapped) < 0 ||
+            PyObject_SetAttrString(self, "__ctype_be__", self) < 0 ||
+            PyObject_SetAttrString(swapped, "__ctype_be__", self) < 0 ||
+            PyObject_SetAttrString(swapped, "__ctype_le__", swapped) < 0)
+       {
+            Py_DECREF(swapped);
+            return -1;
+        }
         /* We are creating the type for the OTHER endian */
         sw_info->format = _ctypes_alloc_format_string("<", stginfo->format+1);
 #else
-        PyObject_SetAttrString(self, "__ctype_be__", swapped);
-        PyObject_SetAttrString(self, "__ctype_le__", self);
-        PyObject_SetAttrString(swapped, "__ctype_le__", self);
-        PyObject_SetAttrString(swapped, "__ctype_be__", swapped);
+        if (PyObject_SetAttrString(self, "__ctype_be__", swapped) < 0 ||
+            PyObject_SetAttrString(self, "__ctype_le__", self) < 0 ||
+            PyObject_SetAttrString(swapped, "__ctype_le__", self) < 0 ||
+            PyObject_SetAttrString(swapped, "__ctype_be__", swapped) < 0)
+        {
+            Py_DECREF(swapped);
+            return -1;
+        }
         /* We are creating the type for the OTHER endian */
         sw_info->format = _ctypes_alloc_format_string(">", stginfo->format+1);
 #endif
         Py_DECREF(swapped);
-        if (PyErr_Occurred()) {
+        if (sw_info->format == NULL) {
             return -1;
         }
     };
diff --git a/Modules/_interpchannelsmodule.c b/Modules/_interpchannelsmodule.c
index 18f892406d10b99..930d7276a3ed45e 100644
--- a/Modules/_interpchannelsmodule.c
+++ b/Modules/_interpchannelsmodule.c
@@ -2638,7 +2638,7 @@ _channelid_shared(PyThreadState *tstate, PyObject *obj, _PyXIData_t *data)
     if (st == NULL) {
         return -1;
     }
-    if (!PyObject_IsInstance(obj, (PyObject *)st->ChannelIDType)) {
+    if (!PyObject_TypeCheck(obj, st->ChannelIDType)) {
         PyErr_Format(PyExc_TypeError,
                      "'_id' attribute must be an %N object, not %T",
                      st->ChannelIDType, obj);
diff --git a/Python/pylifecycle.c b/Python/pylifecycle.c
index 8888f523559123a..5889e146c055091 100644
--- a/Python/pylifecycle.c
+++ b/Python/pylifecycle.c
@@ -3211,8 +3211,14 @@ init_sys_streams(PyThreadState *tstate)
                        config->stdio_errors);
     if (std == NULL)
         goto error;
-    PySys_SetObject("__stdin__", std);
-    _PySys_SetAttr(&_Py_ID(stdin), std);
+    if (PySys_SetObject("__stdin__", std) < 0) {
+        Py_DECREF(std);
+        goto error;
+    }
+    if (_PySys_SetAttr(&_Py_ID(stdin), std) < 0) {
+        Py_DECREF(std);
+        goto error;
+    }
     Py_DECREF(std);
 
     /* Set sys.stdout */
@@ -3222,8 +3228,14 @@ init_sys_streams(PyThreadState *tstate)
                        config->stdio_errors);
     if (std == NULL)
         goto error;
-    PySys_SetObject("__stdout__", std);
-    _PySys_SetAttr(&_Py_ID(stdout), std);
+    if (PySys_SetObject("__stdout__", std) < 0) {
+        Py_DECREF(std);
+        goto error;
+    }
+    if (_PySys_SetAttr(&_Py_ID(stdout), std) < 0) {
+        Py_DECREF(std);
+        goto error;
+    }
     Py_DECREF(std);
 
 #if 1 /* Disable this if you have trouble debugging bootstrap stuff */
diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index ce75027f67e9f4f..99ab232732123fe 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -4380,8 +4380,12 @@ _PySys_Create(PyThreadState *tstate, PyObject **sysmod_p)
     PyUnstable_Module_SetGIL(sysmod, Py_MOD_GIL_NOT_USED);
 #endif
 
-    PyModule_AddIntMacro(sysmod, EXIT_SUCCESS);
-    PyModule_AddIntMacro(sysmod, EXIT_FAILURE);
+    if (Pyodule_AddIntMacro(sysmod, EXIT_SUCCESS) < 0) {
+        goto error;
+    }
+    if (PyModule_AddIntMacro(sysmod, EXIT_FAILURE) < 0) {
+        goto error;
+    }
 
     PyObject *sysdict = PyModule_GetDict(sysmod);
     if (sysdict == NULL) {

From 26d524e9fda296ab9b50f2771db0b6a48ddbc851 Mon Sep 17 00:00:00 2001
From: Stan Ulbrych <stan@python.org>
Date: Sat, 24 Oct 2026 19:45:05 +0100
Subject: [PATCH 2/2] Fix a typo

---
 Python/sysmodule.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/Python/sysmodule.c b/Python/sysmodule.c
index 99ab232732123fe..6f336dac058379e 100644
--- a/Python/sysmodule.c
+++ b/Python/sysmodule.c
@@ -4380,7 +4380,7 @@ _PySys_Create(PyThreadState *tstate, PyObject **sysmod_p)
     PyUnstable_Module_SetGIL(sysmod, Py_MOD_GIL_NOT_USED);
 #endif
 
-    if (Pyodule_AddIntMacro(sysmod, EXIT_SUCCESS) < 0) {
+    if (PyModule_AddIntMacro(sysmod, EXIT_SUCCESS) < 0) {
         goto error;
     }
     if (PyModule_AddIntMacro(sysmod, EXIT_FAILURE) < 0) {