Jan 10, 2026 · Jan 12, 2026 · Jan 12, 2026 · Jan 12, 2026 · Jan 12, 2026 · Jan 13, 2026
diff --git a/Doc/deprecations/pending-removal-in-3.20.rst b/Doc/deprecations/pending-removal-in-3.20.rst
 Pending removal in Python 3.20
 ------------------------------

 * Calling the ``Struct.__new__()`` without required argument now is
  deprecated and will be removed in Python 3.20.  Calling
  :meth:`~object.__init__` method on initialized :class:`~struct.Struct`
  objects is deprecated and will be removed in Python 3.20.

  (Contributed by Sergey B Kirpichev in :gh:`78724`.)

 * The ``__version__``, ``version`` and ``VERSION`` attributes have been
  deprecated in these standard library modules and will be removed in
  Python 3.20. Use :py:data:`sys.version_info` instead.
diff --git a/Doc/whatsnew/3.15.rst b/Doc/whatsnew/3.15.rst

    (Contributed by Bénédikt Tran in :gh:`134978`.)

 * :mod:`struct`:

  * Calling the ``Struct.__new__()`` without required argument now is
    deprecated and will be removed in Python 3.20.  Calling
    :meth:`~object.__init__` method on initialized :class:`~struct.Struct`
    objects is deprecated and will be removed in Python 3.20.

    (Contributed by Sergey B Kirpichev in :gh:`78724`.)

 * ``__version__``

  * The ``__version__``, ``version`` and ``VERSION`` attributes have been
diff --git a/Lib/test/test_inspect/test_inspect.py b/Lib/test/test_inspect/test_inspect.py

    def test_struct_module_has_signatures(self):
        import struct
        self._test_module_has_signatures(struct)
        unsupported_signature = {'Struct'}
        self._test_module_has_signatures(struct, unsupported_signature=unsupported_signature)

    def test_string_module_has_signatures(self):
        import string
diff --git a/Lib/test/test_struct.py b/Lib/test/test_struct.py
        # Struct instance.  This test can be used to detect the leak
        # when running with regrtest -L.
        s = struct.Struct('i')
        s.__init__('ii')
        with self.assertWarns(DeprecationWarning):
            s.__init__('ii')
        self.assertEqual(s.format, 'ii')
        packed = b'\x01\x00\x00\x00\x02\x00\x00\x00'
        self.assertEqual(s.pack(1, 2), packed)
        self.assertEqual(s.unpack(packed), (1, 2))

    def check_sizeof(self, format_str, number_of_codes):
        # The size of 'PyStructObject'
        totalsize = support.calcobjsize('2n3P')
        totalsize = support.calcobjsize('2n3P1?')
        # 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)
            def __init__(self):
                super().__init__('>h')

        my_struct = MyStruct()
        with self.assertWarns(DeprecationWarning):
            my_struct = MyStruct()
        self.assertEqual(my_struct.pack(12345), b'\x30\x39')

    def test_repr(self):
            self.assertListEqual(list(results), [None] * 5)

    def test_operations_on_half_initialized_Struct(self):
        S = struct.Struct.__new__(struct.Struct)
        with self.assertWarns(DeprecationWarning):
            S = struct.Struct.__new__(struct.Struct)

        spam = array.array('b', b' ')
        self.assertRaises(RuntimeError, S.iter_unpack, spam)
diff --git a/Misc/NEWS.d/next/Library/2026-01-10-16-23-21.gh-issue-78724.HZrfSA.rst b/Misc/NEWS.d/next/Library/2026-01-10-16-23-21.gh-issue-78724.HZrfSA.rst
 Calling the ``Struct.__new__()`` without required argument now is deprecated.
 Calling :meth:`~object.__init__` method on initialized :class:`~struct.Struct`
 objects is deprecated.  Patch by Sergey B Kirpichev.
diff --git a/Modules/_struct.c b/Modules/_struct.c
    formatcode *s_codes;
    PyObject *s_format;
    PyObject *weakreflist; /* List of weak references */
    bool init_called;
 } PyStructObject;

 #define PyStructObject_CAST(op)     ((PyStructObject *)(op))
    return -1;
 }

 static int
 s_init(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 %T",
                     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 || kwds)
        && PyErr_WarnEx(PyExc_DeprecationWarning,
                        "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);
    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 = (PyStructObject *)alloc_func(type, 0);
    if (self == NULL) {
        return NULL;
    }
    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 (s_init(self, PyTuple_GET_ITEM(args, 0))) {
            Py_DECREF(self);
            return NULL;
        }
    }
    return self;
    return(PyObject *)self;
 }

 /*[clinic input]
 Struct.__init__

    format: object
    format: object = NULL

 Create a compiled struct object.


 static int
 Struct___init___impl(PyStructObject *self, PyObject *format)
 /*[clinic end generated code: output=b8e80862444e92d0 input=1af78a5f57d82cec]*/
 /*[clinic end generated code: output=b8e80862444e92d0 input=6275ff3f85752dd7]*/
 {
    int ret = 0;

    if (PyUnicode_Check(format)) {
        format = PyUnicode_AsASCIIString(format);
        if (format == NULL)
            return -1;
    if (!format && !self->s_codes) {
        PyErr_SetString(PyExc_TypeError,
                        "Struct() missing required argument 'format' (pos 1)");
        return -1;
    }
    else {
        Py_INCREF(format);
    if (!self->init_called) {
        if (!self->s_codes && s_init(self, format)) {
            return -1;
        }
        self->init_called = true;
        return 0;
    }

    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)));
    if ((self->s_codes && self->init_called)
        && PyErr_WarnEx(PyExc_DeprecationWarning,
                        ("Explicit call of __init__() on "
                         "initialized Struct() is deprecated"), 1))
    {
        return -1;
    }

    Py_SETREF(self->s_format, format);

    ret = prepare_s(self);
    return ret;
    return s_init(self, format);
 }

 static int
    {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},
 };

diff --git a/Modules/clinic/_struct.c.h b/Modules/clinic/_struct.c.h
Original file line number	Diff line number	Diff line change
		@@ -1,6 +1,13 @@
		Pending removal in Python 3.20
		------------------------------

		* Calling the ``Struct.__new__()`` without required argument now is
		deprecated and will be removed in Python 3.20. Calling
		:meth:`~object.__init__` method on initialized :class:`~struct.Struct`
		objects is deprecated and will be removed in Python 3.20.

		(Contributed by Sergey B Kirpichev in :gh:`78724`.)

		* The ``__version__``, ``version`` and ``VERSION`` attributes have been
		deprecated in these standard library modules and will be removed in
		Python 3.20. Use :py:data:`sys.version_info` instead.
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -1167,6 +1167,15 @@ New deprecations

		(Contributed by Bénédikt Tran in :gh:`134978`.)

		* :mod:`struct`:

		* Calling the ``Struct.__new__()`` without required argument now is
		deprecated and will be removed in Python 3.20. Calling
		:meth:`~object.__init__` method on initialized :class:`~struct.Struct`
		objects is deprecated and will be removed in Python 3.20.

		(Contributed by Sergey B Kirpichev in :gh:`78724`.)

		* ``__version__``

		* The ``__version__``, ``version`` and ``VERSION`` attributes have been
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -6268,7 +6268,8 @@ def test_stat_module_has_signatures(self):

		def test_struct_module_has_signatures(self):
		import struct
		self._test_module_has_signatures(struct)
		unsupported_signature = {'Struct'}
		self._test_module_has_signatures(struct, unsupported_signature=unsupported_signature)

		def test_string_module_has_signatures(self):
		import string
Expand Down
Original file line number	Diff line number	Diff line change
Expand Up		@@ -582,11 +582,16 @@ def test_Struct_reinitialization(self):
		# Struct instance. This test can be used to detect the leak
		# when running with regrtest -L.
		s = struct.Struct('i')
		s.__init__('ii')
		with self.assertWarns(DeprecationWarning):
		s.__init__('ii')
skirpichev marked this conversation as resolved. Show resolvedHide resolved
		self.assertEqual(s.format, 'ii')
		packed = b'\x01\x00\x00\x00\x02\x00\x00\x00'
		self.assertEqual(s.pack(1, 2), packed)
		self.assertEqual(s.unpack(packed), (1, 2))

		def check_sizeof(self, format_str, number_of_codes):
		# The size of 'PyStructObject'
		totalsize = support.calcobjsize('2n3P')
		totalsize = support.calcobjsize('2n3P1?')
		# 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)
Expand DownExpand Up		@@ -790,7 +795,8 @@ class MyStruct(struct.Struct):
		def __init__(self):
		super().__init__('>h')

		my_struct = MyStruct()
		with self.assertWarns(DeprecationWarning):
		my_struct = MyStruct()
		self.assertEqual(my_struct.pack(12345), b'\x30\x39')

		def test_repr(self):
Expand DownExpand Up		@@ -824,7 +830,8 @@ def test_endian_table_init_subinterpreters(self):
		self.assertListEqual(list(results), [None] * 5)

		def test_operations_on_half_initialized_Struct(self):
		S = struct.Struct.__new__(struct.Struct)
		with self.assertWarns(DeprecationWarning):
		S = struct.Struct.__new__(struct.Struct)

		spam = array.array('b', b' ')
		self.assertRaises(RuntimeError, S.iter_unpack, spam)
Expand Down
Original file line number	Diff line number	Diff line change
		@@ -0,0 +1,3 @@
		Calling the ``Struct.__new__()`` without required argument now is deprecated.
		Calling :meth:`~object.__init__` method on initialized :class:`~struct.Struct`
		objects is deprecated. Patch by Sergey B Kirpichev.
Original file line number	Diff line number	Diff line change
Expand Up		@@ -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))
Expand DownExpand Up		@@ -1757,30 +1758,68 @@ prepare_s(PyStructObject *self)
		return -1;
		}

		static int
		s_init(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 %T",
		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 \|\| kwds)
		&& PyErr_WarnEx(PyExc_DeprecationWarning,
		"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);
		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 = (PyStructObject *)alloc_func(type, 0);
		if (self == NULL) {
		return NULL;
		}
		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 (s_init(self, PyTuple_GET_ITEM(args, 0))) {
		Py_DECREF(self);
		return NULL;
		}
		}
		return self;
		return(PyObject *)self;
		}

		/*[clinic input]
		Struct.__init__

		format: object
		format: object = NULL

		Create a compiled struct object.

Expand All		@@ -1790,32 +1829,28 @@ to the format string. See help(struct) for more on format strings.

		static int
		Struct___init___impl(PyStructObject self, PyObject format)
		/[clinic end generated code: output=b8e80862444e92d0 input=1af78a5f57d82cec]/
		/[clinic end generated code: output=b8e80862444e92d0 input=6275ff3f85752dd7]/
		{
		int ret = 0;

		if (PyUnicode_Check(format)) {
		format = PyUnicode_AsASCIIString(format);
		if (format == NULL)
		return -1;
		if (!format && !self->s_codes) {
		PyErr_SetString(PyExc_TypeError,
		"Struct() missing required argument 'format' (pos 1)");
		return -1;
		}
		else {
		Py_INCREF(format);
		if (!self->init_called) {
		if (!self->s_codes && s_init(self, format)) {
		return -1;
		}
		self->init_called = true;
		return 0;
		}

		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)));
		if ((self->s_codes && self->init_called)
		&& PyErr_WarnEx(PyExc_DeprecationWarning,
		("Explicit call of __init__() on "
		"initialized Struct() is deprecated"), 1))
		{
		return -1;
		}

		Py_SETREF(self->s_format, format);

		ret = prepare_s(self);
		return ret;
		return s_init(self, format);
		}

		static int
Expand DownExpand Up		@@ -2437,9 +2472,7 @@ 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},
		};

Expand Down