diff --git a/Doc/whatsnew/3.10.rst b/Doc/whatsnew/3.10.rst
@@ -1708,6 +1708,10 @@ New Features
  These functions allow to activate, deactivate and query the state of the garbage collector from C code without
  having to import the :mod:`gc` module.

Porting to Python 3.10
----------------------


diff --git a/Lib/test/test_sys.py b/Lib/test/test_sys.py
@@ -605,11 +605,12 @@ def test_sys_flags(self):
    def assert_raise_on_new_sys_type(self, sys_attr):
        # Users are intentionally prevented from creating new instances of
        # sys.flags, sys.version_info, and sys.getwindowsversion.
        attr_type = type(sys_attr)
        with self.assertRaises(TypeError):
-            attr_type()
        with self.assertRaises(TypeError):
-            attr_type.__new__(attr_type)

    def test_sys_flags_no_instantiation(self):
        self.assert_raise_on_new_sys_type(sys.flags)

diff --git a/Misc/NEWS.d/next/C API/2021-04-29-17-35-48.bpo-43916.wvWt23.rst b/Misc/NEWS.d/next/C API/2021-04-29-17-35-48.bpo-43916.wvWt23.rst
@@ -0,0 +1,2 @@
diff --git a/Modules/_curses_panel.c b/Modules/_curses_panel.c
@@ -520,7 +520,7 @@ static PyType_Slot PyCursesPanel_Type_slots[] = {
static PyType_Spec PyCursesPanel_Type_spec = {
    .name = "_curses_panel.panel",
    .basicsize = sizeof(PyCursesPanelObject),
-    .flags = Py_TPFLAGS_DEFAULT,
    .slots = PyCursesPanel_Type_slots
};

@@ -656,7 +656,6 @@ _curses_panel_exec(PyObject *mod)
    if (state->PyCursesPanel_Type == NULL) {
        return -1;
    }
-    ((PyTypeObject *)state->PyCursesPanel_Type)->tp_new = NULL;

    if (PyModule_AddType(mod, state->PyCursesPanel_Type) < 0) {
        return -1;

diff --git a/Modules/_cursesmodule.c b/Modules/_cursesmodule.c
@@ -4793,25 +4793,18 @@ PyInit__curses(void)
#ifdef NCURSES_VERSION
    /* ncurses_version */
    if (NcursesVersionType.tp_name == NULL) {
-        if (PyStructSequence_InitType2(&NcursesVersionType,
-                                       &ncurses_version_desc) < 0)
            return NULL;
    }
    v = make_ncurses_version();
    if (v == NULL) {
        return NULL;
    }
    PyDict_SetItemString(d, "ncurses_version", v);
    Py_DECREF(v);
-
-    /* prevent user from creating new instances */
-    NcursesVersionType.tp_init = NULL;
-    NcursesVersionType.tp_new = NULL;
-    if (PyDict_DelItemString(NcursesVersionType.tp_dict, "__new__") < 0 &&
-        PyErr_ExceptionMatches(PyExc_KeyError))
-    {
-        PyErr_Clear();
-    }
#endif /* NCURSES_VERSION */

    SetDictInt("ERR", ERR);

diff --git a/Modules/_tkinter.c b/Modules/_tkinter.c
@@ -1002,7 +1002,7 @@ static PyType_Spec PyTclObject_Type_spec = {
    "_tkinter.Tcl_Obj",
    sizeof(PyTclObject),
    0,
-    Py_TPFLAGS_DEFAULT,
    PyTclObject_Type_slots,
};

@@ -3294,7 +3294,7 @@ static PyType_Spec Tktt_Type_spec = {
    "_tkinter.tktimertoken",
    sizeof(TkttObject),
    0,
-    Py_TPFLAGS_DEFAULT,
    Tktt_Type_slots,
};

@@ -3349,7 +3349,7 @@ static PyType_Spec Tkapp_Type_spec = {
    "_tkinter.tkapp",
    sizeof(TkappObject),
    0,
-    Py_TPFLAGS_DEFAULT,
    Tkapp_Type_slots,
};

@@ -3537,7 +3537,6 @@ PyInit__tkinter(void)
        Py_DECREF(m);
        return NULL;
    }
-    ((PyTypeObject *)o)->tp_new = NULL;
    if (PyModule_AddObject(m, "TkappType", o)) {
        Py_DECREF(o);
        Py_DECREF(m);
@@ -3550,7 +3549,6 @@ PyInit__tkinter(void)
        Py_DECREF(m);
        return NULL;
    }
-    ((PyTypeObject *)o)->tp_new = NULL;
    if (PyModule_AddObject(m, "TkttType", o)) {
        Py_DECREF(o);
        Py_DECREF(m);
@@ -3563,7 +3561,6 @@ PyInit__tkinter(void)
        Py_DECREF(m);
        return NULL;
    }
-    ((PyTypeObject *)o)->tp_new = NULL;
    if (PyModule_AddObject(m, "Tcl_Obj", o)) {
        Py_DECREF(o);
        Py_DECREF(m);

diff --git a/Modules/_xxsubinterpretersmodule.c b/Modules/_xxsubinterpretersmodule.c
@@ -1780,7 +1780,12 @@ static PyTypeObject ChannelIDtype = {
    0,                              /* tp_getattro */
    0,                              /* tp_setattro */
    0,                              /* tp_as_buffer */
-    Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE, /* tp_flags */
    channelid_doc,                  /* tp_doc */
    0,                              /* tp_traverse */
    0,                              /* tp_clear */
@@ -1791,19 +1796,6 @@ static PyTypeObject ChannelIDtype = {
    0,                              /* tp_methods */
    0,                              /* tp_members */
    channelid_getsets,              /* tp_getset */
-    0,                              /* tp_base */
-    0,                              /* tp_dict */
-    0,                              /* tp_descr_get */
-    0,                              /* tp_descr_set */
-    0,                              /* tp_dictoffset */
-    0,                              /* tp_init */
-    0,                              /* tp_alloc */
-    // Note that we do not set tp_new to channelid_new.  Instead we
-    // set it to NULL, meaning it cannot be instantiated from Python
-    // code.  We do this because there is a strong relationship between
-    // channel IDs and the channel lifecycle, so this limitation avoids
-    // related complications.
-    NULL,                           /* tp_new */
};



diff --git a/Objects/structseq.c b/Objects/structseq.c
@@ -459,8 +459,10 @@ initialize_members(PyStructSequence_Desc *desc, PyMemberDef* members,
    members[k].name = NULL;
}

int
-PyStructSequence_InitType2(PyTypeObject *type, PyStructSequence_Desc *desc)
{
    PyMemberDef *members;
    Py_ssize_t n_members, n_unnamed_members;
@@ -488,7 +490,7 @@ PyStructSequence_InitType2(PyTypeObject *type, PyStructSequence_Desc *desc)
    type->tp_base = &PyTuple_Type;
    type->tp_methods = structseq_methods;
    type->tp_new = structseq_new;
-    type->tp_flags = Py_TPFLAGS_DEFAULT | Py_TPFLAGS_HAVE_GC;
    type->tp_traverse = (traverseproc) structseq_traverse;

    n_members = count_members(desc, &n_unnamed_members);
@@ -516,6 +518,12 @@ PyStructSequence_InitType2(PyTypeObject *type, PyStructSequence_Desc *desc)
    return 0;
}

void
PyStructSequence_InitType(PyTypeObject *type, PyStructSequence_Desc *desc)
{
-Original file line number
+Diff line change
@@ Expand Up / @@ -1708,6 +1708,10 @@ New Features @@
       These functions allow to activate, deactivate and query the state of the garbage collector from C code without
       having to import the :mod:`gc` module.
     Porting to Python 3.10
     ----------------------
@@ Expand Down @@