gh-154387: fix structseq_repr by labeling unnamed fields in repr as <unnamed@N>

Lib/test/test_structseq.py

@@ -6,7 +6,7 @@
 import textwrap
 import time
 import unittest
-from test.support import script_helper
+from test.support import import_helper, script_helper
 
 
 class StructSeqTest(unittest.TestCase):
@@ -48,6 +48,105 @@ def test_repr(self):
         self.assertIn("st_ino=", rep)
         self.assertIn("st_dev=", rep)
 
+    def test_repr_with_unnamed_fields(self):
+        # gh-154387: each unnamed field is shown at its own index rather than
+        # borrowing a neighbour's name. Unnamed fields need not be contiguous or
+        # trailing.
+        _testcapi = import_helper.import_module("_testcapi")
+        cls = _testcapi.structseq_newtype_interspersed_unnamed()
+        self.assertEqual(cls.n_fields, 5)
+        self.assertEqual(cls.n_sequence_fields, 4)
+        self.assertEqual(cls.n_unnamed_fields, 2)
+        self.assertEqual(cls.__match_args__, ("first", "third"))
+
+        t1 = cls(range(5))
+        self.assertEqual(repr(t1),
+            "_testcapi.Interspersed(first=0, <unnamed@1>=1, third=2, "
+            "<unnamed@3>=3)")
+        # Only the visible fields form the tuple; the hidden "fifth" is excluded.
+        self.assertEqual(tuple(t1), (0, 1, 2, 3))
+        self.assertEqual(len(t1), 4)
+        # Named fields are accessible by attribute, including the hidden one.
+        self.assertEqual(t1.first, 0)
+        self.assertEqual(t1.third, 2)
+        self.assertEqual(t1.fifth, 4)
+
+        t2 = cls(range(4))
+        self.assertEqual(repr(t2),
+            "_testcapi.Interspersed(first=0, <unnamed@1>=1, third=2, "
+            "<unnamed@3>=3)")
+        # Only the visible fields form the tuple; the hidden "fifth" is excluded.
+        self.assertEqual(tuple(t2), (0, 1, 2, 3))
+        self.assertEqual(len(t2), 4)
+        # Named fields are accessible by attribute, including the hidden one.
+        # The hidden "fifth" is not set, so it returns None.
+        self.assertEqual(t2.first, 0)
+        self.assertEqual(t2.third, 2)
+        self.assertIsNone(t2.fifth)
+
+    def test_os_stat_result_has_custom_repr(self):
+        # gh-154387: os.stat_result has a custom repr (statresult_repr) showing
+        # the float times st_atime/st_mtime/st_ctime by name, not the unnamed
+        # integer slots with generic "<unnamed@N>".
+        self.assertEqual(os.stat_result.n_sequence_fields, 10)
+        self.assertEqual(os.stat_result.n_unnamed_fields, 3)
+
+        # All fields supplied: st_atime/st_mtime/st_ctime are the float slots.
+        r1 = os.stat_result(range(os.stat_result.n_fields))
+        rep = repr(r1)
+        self.assertEqual(rep,
+            "os.stat_result(st_mode=0, st_ino=1, st_dev=2, st_nlink=3, "
+            "st_uid=4, st_gid=5, st_size=6, st_atime=10, st_mtime=11, "
+            "st_ctime=12)")
+        self.assertNotIn("<unnamed@", rep)
+        self.assertEqual(r1.st_atime, 10)
+        self.assertEqual(r1.st_mtime, 11)
+        self.assertEqual(r1.st_ctime, 12)
+
+        # Only the visible slots supplied: statresult_new fills the float times
+        # from the integer slots, so the repr shows those filled values.
+        r2 = os.stat_result(range(10))
+        self.assertEqual(repr(r2),
+            "os.stat_result(st_mode=0, st_ino=1, st_dev=2, st_nlink=3, "
+            "st_uid=4, st_gid=5, st_size=6, st_atime=7, st_mtime=8, "
+            "st_ctime=9)")
+        self.assertEqual(r2.st_atime, 7)
+        self.assertEqual(r2.st_mtime, 8)
+        self.assertEqual(r2.st_ctime, 9)
+
+        # The st_atime/st_mtime slots are supplied, but st_ctime is not; the
+        # st_ctime float slot is filled from the st_ctime integer slot.
+        r3 = os.stat_result(range(12))
+        self.assertEqual(repr(r3),
+            "os.stat_result(st_mode=0, st_ino=1, st_dev=2, st_nlink=3, "
+            "st_uid=4, st_gid=5, st_size=6, st_atime=10, st_mtime=11, "
+            "st_ctime=9)")
+        self.assertEqual(r3.st_atime, 10)
+        self.assertEqual(r3.st_mtime, 11)
+        self.assertEqual(r3.st_ctime, 9)
+
+        # The st_mtime slot is supplied, but st_atime/st_ctime are not; the
+        # st_atime/st_ctime float slots are filled from the st_atime/st_ctime
+        # integer slots.
+        r4 = os.stat_result(range(10), {'st_mtime': -1.0})
+        self.assertEqual(repr(r4),
+            "os.stat_result(st_mode=0, st_ino=1, st_dev=2, st_nlink=3, "
+            "st_uid=4, st_gid=5, st_size=6, st_atime=7, st_mtime=-1.0, "
+            "st_ctime=9)")
+        self.assertEqual(r4.st_atime, 7)
+        self.assertEqual(r4.st_mtime, -1.0)
+        self.assertEqual(r4.st_ctime, 9)
+
+        # repr(), __repr__(), and str() must all resolve to the custom repr
+        # (a raw tp_repr override left __repr__() diverging).
+        for r in (r1, r2, r3, r4):
+            rep = repr(r)
+            self.assertEqual(r.__repr__(), rep)
+            self.assertEqual(type(r).__repr__(r), rep)
+            self.assertEqual(str(r), rep)
+            self.assertEqual(f"{r!r}", rep)
+            self.assertEqual(f"{r!s}", rep)
+
     def test_concat(self):
         t1 = time.gmtime()
         t2 = t1 + tuple(t1)

Misc/NEWS.d/next/Core_and_Builtins/2026-07-25-14-06-33.gh-issue-154387.t2fIXs.rst

@@ -0,0 +1,6 @@
+Fix the :func:`repr` of struct sequence objects that contain unnamed fields,
+such as :class:`os.stat_result`, whose integer time slots previously borrowed
+the ``st_atime``/``st_mtime``/``st_ctime`` names of separate hidden float
+fields. Unnamed fields are now shown as ``<unnamed@N>`` (``N`` is the sequence
+index); :class:`os.stat_result` uses a dedicated repr that shows the float
+``st_atime``, ``st_mtime`` and ``st_ctime`` fields by name. Patch by Xuehai Pan.

Modules/_testcapimodule.c

@@ -1304,6 +1304,28 @@ test_structseq_newtype_null_descr_doc(PyObject *Py_UNUSED(self),
     Py_RETURN_NONE;
 }
 
+static PyObject *
+structseq_newtype_interspersed_unnamed(PyObject *Py_UNUSED(self),
+                              PyObject *Py_UNUSED(args))
+{
+    // gh-154387: unnamed fields may appear anywhere among the visible fields
+    // (here at indices 1 and 3), and a named field may be hidden (here "fifth"
+    // at index 4, since n_in_sequence is 4).
+    PyStructSequence_Field descr_fields[] = {
+        {"first", "field 0"},
+        {PyStructSequence_UnnamedField, "field 1"},
+        {"third", "field 2"},
+        {PyStructSequence_UnnamedField, "field 3"},
+        {"fifth", "field 4"},
+        {NULL, NULL},
+    };
+    PyStructSequence_Desc descr = {
+        "_testcapi.Interspersed", NULL, descr_fields, 4,
+    };
+
+    return (PyObject *)PyStructSequence_NewType(&descr);
+}
+
 typedef struct {
     PyThread_type_lock start_event;
     PyThread_type_lock exit_event;
@@ -3007,6 +3029,8 @@ static PyMethodDef TestMethods[] = {
         test_structseq_newtype_doesnt_leak, METH_NOARGS},
     {"test_structseq_newtype_null_descr_doc",
         test_structseq_newtype_null_descr_doc, METH_NOARGS},
+    {"structseq_newtype_interspersed_unnamed",
+        structseq_newtype_interspersed_unnamed, METH_NOARGS},
     {"pyobject_repr_from_null", pyobject_repr_from_null, METH_NOARGS},
     {"pyobject_str_from_null",  pyobject_str_from_null, METH_NOARGS},
     {"pyobject_bytes_from_null", pyobject_bytes_from_null, METH_NOARGS},

Modules/posixmodule.c

@@ -2572,6 +2572,8 @@ statresult_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     /* If we have been initialized from a tuple,
        st_?time might be set to None. Initialize it
        from the int slots.  */
+    /* See also statresult_repr() below, which assumes that the float slots are
+       always initialized. */
     for (i = 7; i <= 9; i++) {
         if (result->ob_item[i+3] == Py_None) {
             Py_DECREF(Py_None);
@@ -2581,6 +2583,63 @@ statresult_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     return (PyObject*)result;
 }
 
+static PyObject *
+statresult_repr(PyObject *op, PyObject *Py_UNUSED(ignored))
+{
+    // gh-154387: Show the unnamed integer slots 7-9 with following named float
+    // slots st_atime/st_mtime/st_ctime instead of the generic "<unnamed@N>".
+    // The custom statresult_new() above always initializes the float slots.
+    // So it is safe to use the float slots for the repr().
+    PyTypeObject *type = Py_TYPE(op);
+    PyUnicodeWriter *writer = PyUnicodeWriter_Create(128);
+    if (writer == NULL) {
+        return NULL;
+    }
+    if (PyUnicodeWriter_WriteUTF8(writer, type->tp_name, -1) < 0) {
+        goto error;
+    }
+    if (PyUnicodeWriter_WriteChar(writer, '(') < 0) {
+        goto error;
+    }
+    // The first 10 packed members: st_mode..st_size and the 3 float times
+    // st_atime/st_mtime/st_ctime (tp_members omits the unnamed slots 7-9).
+    // NB: This approach assumes the 3 unnamed slots are at the end of the
+    // visible members, which is true for the current stat_result_desc.
+    for (Py_ssize_t i = 0; i < 10; i++) {
+        if (i > 0 && PyUnicodeWriter_WriteUTF8(writer, ", ", 2) < 0) {
+            goto error;
+        }
+        PyMemberDef *member = &type->tp_members[i];
+        if (PyUnicodeWriter_WriteUTF8(writer, member->name, -1) < 0) {
+            goto error;
+        }
+        if (PyUnicodeWriter_WriteChar(writer, '=') < 0) {
+            goto error;
+        }
+        PyObject *value = PyMember_GetOne((const char *)op, member);
+        if (value == NULL) {
+            goto error;
+        }
+        if (PyUnicodeWriter_WriteRepr(writer, value) < 0) {
+            Py_DECREF(value);
+            goto error;
+        }
+        Py_DECREF(value);
+    }
+    if (PyUnicodeWriter_WriteChar(writer, ')') < 0) {
+        goto error;
+    }
+    return PyUnicodeWriter_Finish(writer);
+
+error:
+    PyUnicodeWriter_Discard(writer);
+    return NULL;
+}
+
+static PyMethodDef statresult_repr_methoddef = {
+    "__repr__", statresult_repr, METH_NOARGS, NULL,
+};
+
 static int
 _posix_clear(PyObject *module)
 {
@@ -18875,6 +18934,20 @@ posixmodule_exec(PyObject *m)
     }
     state->statresult_new_orig = ((PyTypeObject *)state->StatResultType)->tp_new;
     ((PyTypeObject *)state->StatResultType)->tp_new = statresult_new;
+    // Install __repr__ through the type dict so repr() and st.__repr__()
+    // resolve to the same function; a raw type->tp_repr assignment leaves the
+    // stale __repr__ wrapper which is readied by PyStructSequence_NewType.
+    PyObject *statresult_repr_descr = PyDescr_NewMethod(
+        (PyTypeObject *)state->StatResultType, &statresult_repr_methoddef);
+    if (statresult_repr_descr == NULL) {
+        return -1;
+    }
+    if (PyObject_SetAttrString(state->StatResultType, "__repr__",
+                               statresult_repr_descr) < 0) {
+        Py_DECREF(statresult_repr_descr);
+        return -1;
+    }
+    Py_DECREF(statresult_repr_descr);
 
     state->StatVFSResultType = (PyObject *)PyStructSequence_NewType(&statvfs_result_desc);
     if (PyModule_AddObjectRef(m, "statvfs_result", state->StatVFSResultType) < 0) {

Objects/structseq.c

@@ -275,11 +275,11 @@ structseq_repr(PyObject *op)
 {
     PyStructSequence *obj = (PyStructSequence *)op;
     PyTypeObject *typ = Py_TYPE(obj);
+    Py_ssize_t n_visible_fields = VISIBLE_SIZE(obj);
 
     // count 5 characters per item: "x=1, "
     Py_ssize_t type_name_len = strlen(typ->tp_name);
-    Py_ssize_t prealloc = (type_name_len + 1
-                           + VISIBLE_SIZE(obj) * 5 + 1);
+    Py_ssize_t prealloc = type_name_len + 1 + n_visible_fields * 5 + 1;
     PyUnicodeWriter *writer = PyUnicodeWriter_Create(prealloc);
     if (writer == NULL) {
         return NULL;
@@ -293,7 +293,10 @@ structseq_repr(PyObject *op)
         goto error;
     }
 
-    for (Py_ssize_t i=0; i < VISIBLE_SIZE(obj); i++) {
+    // Unnamed slots have no tp_members entry; match each member to its slot by
+    // offset so unnamed slots print "<unnamed@i>", not a later name (gh-154387).
+    Py_ssize_t member_index = 0;
+    for (Py_ssize_t i = 0; i < n_visible_fields; i++) {
         if (i > 0) {
             // Write ", "
             if (PyUnicodeWriter_WriteChar(writer, ',') < 0) {
@@ -304,16 +307,26 @@ structseq_repr(PyObject *op)
             }
         }
 
-        // Write name
-        const char *name_utf8 = typ->tp_members[i].name;
-        if (name_utf8 == NULL) {
-            PyErr_Format(PyExc_SystemError,
-                         "In structseq_repr(), member %zd name is NULL"
-                         " for type %.500s", i, typ->tp_name);
-            goto error;
+        // The named member's slot is recovered from its offset.
+        const PyMemberDef *member = &typ->tp_members[member_index];
+        Py_ssize_t named_slot = -1;
+        if (member->name != NULL) {
+            // Recover the true slot index. See also function `initialize_members` below.
+            named_slot = (member->offset - (Py_ssize_t)offsetof(PyStructSequence, ob_item))
+                           / sizeof(PyObject *);
         }
-        if (PyUnicodeWriter_WriteUTF8(writer, name_utf8, -1) < 0) {
-            goto error;
+
+        // Write the field name, or "<unnamed@i>" for an unnamed field.
+        if (named_slot == i) {
+            if (PyUnicodeWriter_WriteUTF8(writer, member->name, -1) < 0) {
+                goto error;
+            }
+            member_index++;
+        }
+        else {
+            if (PyUnicodeWriter_Format(writer, "<unnamed@%zd>", i) < 0) {
+                goto error;
+            }
         }
 
         // Write "=" + repr(value)