bpo-43916: Add Py_TPFLAGS_DISALLOW_INSTANTIATION type flag (GH-25721)
Add a new Py_TPFLAGS_DISALLOW_INSTANTIATION type flag to disallow
creating type instances: set tp_new to NULL and don't create the
"__new__" key in the type dictionary.
The flag is set automatically on static types if tp_base is NULL or
&PyBaseObject_Type and tp_new is NULL.
Use the flag on the following types:
* _curses.ncurses_version type
* _curses_panel.panel
* _tkinter.Tcl_Obj
* _tkinter.tkapp
* _tkinter.tktimertoken
* _xxsubinterpretersmodule.ChannelID
* sys.flags type
* sys.getwindowsversion() type
* sys.version_info type
Update MyStr example in the C API documentation to use
Py_TPFLAGS_DISALLOW_INSTANTIATION.
Add _PyStructSequence_InitType() function to create a structseq type
with the Py_TPFLAGS_DISALLOW_INSTANTIATION flag set.
type_new() calls _PyType_CheckConsistency() at exit.
diff --git a/Modules/_xxsubinterpretersmodule.c b/Modules/_xxsubinterpretersmodule.c
index b94b130..9290255 100644
--- 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 */
+ // Use Py_TPFLAGS_DISALLOW_INSTANTIATION so the type 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. Use the _channel_id() function instead.
+ Py_TPFLAGS_DEFAULT | Py_TPFLAGS_BASETYPE
+ | Py_TPFLAGS_DISALLOW_INSTANTIATION, /* 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 */
};