[3.13] gh-145623: Fix crashes on uninitialized struct.Struct objects (gh-145624) (GH-145631)

Author: raminfp

Lib/test/test_struct.py

@@ -806,6 +806,8 @@ def test_operations_on_half_initialized_Struct(self):
         self.assertRaises(RuntimeError, S.unpack, spam)
         self.assertRaises(RuntimeError, S.unpack_from, spam)
         self.assertRaises(RuntimeError, getattr, S, 'format')
+        self.assertRaises(RuntimeError, S.__sizeof__)
+        self.assertRaises(RuntimeError, repr, S)
         self.assertEqual(S.size, -1)
 
 

Misc/NEWS.d/next/Library/2026-03-07-15-00-00.gh-issue-145623.2Y7LzT.rst

@@ -0,0 +1,3 @@
+Fix crash in :mod:`struct` when calling :func:`repr` or
+``__sizeof__()`` on an uninitialized :class:`struct.Struct`
+object created via ``Struct.__new__()`` without calling ``__init__()``.

Modules/_struct.c

@@ -2196,6 +2196,7 @@ PyDoc_STRVAR(s_sizeof__doc__,
 static PyObject *
 s_sizeof(PyStructObject *self, void *unused)
 {
+    ENSURE_STRUCT_IS_READY(self);
     size_t size = _PyObject_SIZE(Py_TYPE(self)) + sizeof(formatcode);
     for (formatcode *code = self->s_codes; code->fmtdef != NULL; code++) {
         size += sizeof(formatcode);
@@ -2206,6 +2207,7 @@ s_sizeof(PyStructObject *self, void *unused)
 static PyObject *
 s_repr(PyStructObject *self)
 {
+    ENSURE_STRUCT_IS_READY(self);
     PyObject* fmt = PyUnicode_FromStringAndSize(
         PyBytes_AS_STRING(self->s_format), PyBytes_GET_SIZE(self->s_format));
     if (fmt == NULL) {