add init_called flag

python · serhiy-storchaka · Mar 12, 2026 · Jan 10, 2026 · Jan 12, 2026 · Jan 12, 2026
commit babb274bfe004bdaed46c2437a5e1ab25aa1842a
diff --git a/Lib/test/test_struct.py b/Lib/test/test_struct.py
@@ -584,7 +584,7 @@ def test_Struct_reinitialization(self):
 
     def check_sizeof(self, format_str, number_of_codes):
         # The size of 'PyStructObject'
-        totalsize = support.calcobjsize('2n3P')
+        totalsize = support.calcobjsize('2n3P1?')
-        totalsize = support.calcobjsize('2n3P1?')
+        totalsize = support.calcobjsize('2n3P?')
-        totalsize = support.calcobjsize('2n3P1?')
+        totalsize = support.calcobjsize('2n3P?')
         # The size taken up by the 'formatcode' dynamic array
         totalsize += struct.calcsize('P3n0P') * (number_of_codes + 1)
         support.check_sizeof(self, struct.Struct(format_str), totalsize)

diff --git a/Modules/_struct.c b/Modules/_struct.c
@@ -70,6 +70,7 @@ typedef struct {
     formatcode *s_codes;
     PyObject *s_format;
     PyObject *weakreflist; /* List of weak references */
+    bool init_called;
 } PyStructObject;
 
 #define PyStructObject_CAST(op)     ((PyStructObject *)(op))
@@ -1757,30 +1758,61 @@ prepare_s(PyStructObject *self)
     return -1;
 }
 
+static int
+actual___init___impl(PyStructObject *self, PyObject *format)
+{
+    if (PyUnicode_Check(format)) {
+        format = PyUnicode_AsASCIIString(format);
+        if (format == NULL)
+            return -1;
+    }
+    else {
+        Py_INCREF(format);
+    }
+    if (!PyBytes_Check(format)) {
+        Py_DECREF(format);
+        PyErr_Format(PyExc_TypeError,
+                     "Struct() argument 1 must be a str or bytes object, "
+                     "not %.200s",
+                     _PyType_Name(Py_TYPE(format)));
+        return -1;
+    }
+    Py_SETREF(self->s_format, format);
+    if (prepare_s(self)) {
+        return -1;
+    }
+    return 0;
+}
+
 static PyObject *
 s_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 {
-    PyObject *self;
+    PyStructObject *self;
 
-    if (PyTuple_GET_SIZE(args) != 1
+    if ((PyTuple_GET_SIZE(args) != 1 || kwds)
         && PyErr_WarnEx(PyExc_DeprecationWarning,
-                        "Struct().__new__() has one required argument", 1))
+                        "Struct.__new__() has one positional argument", 1))
     {
         return NULL;
     }
     assert(type != NULL);
     allocfunc alloc_func = PyType_GetSlot(type, Py_tp_alloc);
     assert(alloc_func != NULL);
-
-    self = alloc_func(type, 0);
+    self = (PyStructObject *)alloc_func(type, 0);
     if (self != NULL) {
-        PyStructObject *s = (PyStructObject*)self;
-        s->s_format = Py_NewRef(Py_None);
-        s->s_codes = NULL;
-        s->s_size = -1;
-        s->s_len = -1;
+        self->s_format = Py_NewRef(Py_None);
+        self->s_codes = NULL;
+        self->s_size = -1;
+        self->s_len = -1;
+        self->init_called = false;
+        if (PyTuple_GET_SIZE(args) > 0) {
+            if (actual___init___impl(self, PyTuple_GET_ITEM(args, 0))) {
+                Py_DECREF(self);
+                return NULL;
+            }
+        }
     }
-    return self;
+    return (PyObject *)self;
 }
 
 /*[clinic input]
@@ -1800,37 +1832,21 @@ static int
 Struct___init___impl(PyStructObject *self, PyObject *format)
 /*[clinic end generated code: output=b8e80862444e92d0 input=192a4575a3dde802]*/
 {
-    int ret = 0;
-
-    if (self->s_codes
+    if (!self->init_called) {
+        if (!self->s_codes && actual___init___impl(self, format)) {
+            return -1;
+        }
+        self->init_called = true;
+        return 0;
+    }
+    if ((self->s_codes && self->init_called)
         && PyErr_WarnEx(PyExc_DeprecationWarning,
                         ("Explicit call of __init__() on "
                          "initialized Struct() is deprecated"), 1))
     {
         return -1;
     }
-    if (PyUnicode_Check(format)) {
-        format = PyUnicode_AsASCIIString(format);
-        if (format == NULL)
-            return -1;
-    }
-    else {
-        Py_INCREF(format);
-    }
-
-    if (!PyBytes_Check(format)) {
-        Py_DECREF(format);
-        PyErr_Format(PyExc_TypeError,
-                     "Struct() argument 1 must be a str or bytes object, "
-                     "not %.200s",
-                     _PyType_Name(Py_TYPE(format)));
-        return -1;
-    }
-
-    Py_SETREF(self->s_format, format);
-
-    ret = prepare_s(self);
-    return ret;
+    return actual___init___impl(self, format);
 }
 
 static int
@@ -2473,9 +2489,7 @@ static PyType_Slot PyStructType_slots[] = {
     {Py_tp_members, s_members},
     {Py_tp_getset, s_getsetlist},
     {Py_tp_init, Struct___init__},
-    {Py_tp_alloc, PyType_GenericAlloc},
     {Py_tp_new, s_new},
-    {Py_tp_free, PyObject_GC_Del},
     {0, 0},
 };