gh-128762: Include inline values in sys.getsizeof()

Lib/test/test_sys.py

@@ -31,6 +31,10 @@ def requires_subinterpreters(meth):
     return unittest.skipIf(interpreters is None,
                            'subinterpreters required')(meth)
 
+class ObjectWithValue:
+    value: ObjectWithValue | None
+    def __init__(self, value):
+        self.value = value
 
 DICT_KEY_STRUCT_FORMAT = 'n2BI2n'
 
@@ -1475,6 +1479,16 @@ def test_gc_head_size(self):
         # but lists are
         self.assertEqual(sys.getsizeof([]), vsize('Pn') + gc_header_size)
 
+    def test_inline_values(self):
+        vsize = test.support.calcvobjsize
+        gc_header_size = self.gc_headsize
+        inline_values_size = 32
+
+        linked_list = None
+        for i in range(28):
+            linked_list = ObjectWithValue(linked_list)
+        self.assertEqual(sys.getsizeof(linked_list), vsize('P') + gc_header_size + inline_values_size)
+
     def test_errors(self):
         class BadSizeof:
             def __sizeof__(self):

Misc/NEWS.d/next/Core_and_Builtins/2025-01-12-13-38-23.gh-issue-128762.O3iYBW.rst

@@ -0,0 +1 @@
+`sys.getsizeof()` now accounts for inline values stored alongside the object

Python/sysmodule.c

@@ -1842,10 +1842,11 @@ _PySys_GetSizeOf(PyObject *o)
     PyObject *res = NULL;
     PyObject *method;
     Py_ssize_t size;
+    PyTypeObject *type = Py_TYPE(o);
     PyThreadState *tstate = _PyThreadState_GET();
 
     /* Make sure the type is initialized. float gets initialized late */
-    if (PyType_Ready(Py_TYPE(o)) < 0) {
+    if (PyType_Ready(type) < 0) {
         return (size_t)-1;
     }
 
@@ -1854,7 +1855,7 @@ _PySys_GetSizeOf(PyObject *o)
         if (!_PyErr_Occurred(tstate)) {
             _PyErr_Format(tstate, PyExc_TypeError,
                           "Type %.100s doesn't define __sizeof__",
-                          Py_TYPE(o)->tp_name);
+                          type->tp_name);
         }
     }
     else {
@@ -1876,6 +1877,10 @@ _PySys_GetSizeOf(PyObject *o)
         return (size_t)-1;
     }
 
+    if (type->tp_flags & Py_TPFLAGS_INLINE_VALUES) {
+        size += _PyInlineValuesSize(type);
+    }
+
     size_t presize = 0;
     if (!Py_IS_TYPE(o, &PyType_Type) ||
          PyType_HasFeature((PyTypeObject *)o, Py_TPFLAGS_HEAPTYPE))