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bpo-43916: Add Py_TPFLAGS_DISALLOW_INSTANTIATION type flag (GH-25721)

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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.
This commit is contained in:
Victor Stinner 2021-04-30 12:46:15 +02:00 • committed by GitHub
parent b73b5fb9ea
commit 3bb09947ec
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GPG key ID: 4AEE18F83AFDEB23
13 changed files with 144 additions and 102 deletions
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15
Modules/_cursesmodule.c
View file

@ -4793,9 +4793,11 @@ PyInit__curses(void)
#ifdef NCURSES_VERSION
/* ncurses_version */
if (NcursesVersionType.tp_name == NULL) {
if (PyStructSequence_InitType2(&NcursesVersionType,
&ncurses_version_desc) < 0)
if (_PyStructSequence_InitType(&NcursesVersionType,
&ncurses_version_desc,
Py_TPFLAGS_DISALLOW_INSTANTIATION) < 0) {
return NULL;
}
}
v = make_ncurses_version();
if (v == NULL) {
@ -4803,15 +4805,6 @@ PyInit__curses(void)
}
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);