diff --git a/Misc/NEWS.d/next/Tools-Demos/2022-04-20-14-26-14.gh-issue-91583.200qI0.rst b/Misc/NEWS.d/next/Tools-Demos/2022-04-20-14-26-14.gh-issue-91583.200qI0.rst
new file mode 100644
index 00000000000000..bdfa71100f95ae
--- /dev/null
+++ b/Misc/NEWS.d/next/Tools-Demos/2022-04-20-14-26-14.gh-issue-91583.200qI0.rst
@@ -0,0 +1,2 @@
+Fix regression in the code generated by Argument Clinic for functions with
+the ``defining_class`` parameter.
diff --git a/Modules/clinic/_curses_panel.c.h b/Modules/clinic/_curses_panel.c.h
index 45898070b1f543..e4642b58332de0 100644
--- a/Modules/clinic/_curses_panel.c.h
+++ b/Modules/clinic/_curses_panel.c.h
@@ -17,18 +17,11 @@ _curses_panel_panel_bottom_impl(PyCursesPanelObject *self, PyTypeObject *cls);
 static PyObject *
 _curses_panel_panel_bottom(PyCursesPanelObject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":bottom", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "bottom() takes no arguments");
+        return NULL;
     }
-    return_value = _curses_panel_panel_bottom_impl(self, cls);
-
-exit:
-    return return_value;
+    return _curses_panel_panel_bottom_impl(self, cls);
 }
 
 PyDoc_STRVAR(_curses_panel_panel_hide__doc__,
@@ -48,18 +41,11 @@ _curses_panel_panel_hide_impl(PyCursesPanelObject *self, PyTypeObject *cls);
 static PyObject *
 _curses_panel_panel_hide(PyCursesPanelObject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":hide", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "hide() takes no arguments");
+        return NULL;
     }
-    return_value = _curses_panel_panel_hide_impl(self, cls);
-
-exit:
-    return return_value;
+    return _curses_panel_panel_hide_impl(self, cls);
 }
 
 PyDoc_STRVAR(_curses_panel_panel_show__doc__,
@@ -77,18 +63,11 @@ _curses_panel_panel_show_impl(PyCursesPanelObject *self, PyTypeObject *cls);
 static PyObject *
 _curses_panel_panel_show(PyCursesPanelObject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":show", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "show() takes no arguments");
+        return NULL;
     }
-    return_value = _curses_panel_panel_show_impl(self, cls);
-
-exit:
-    return return_value;
+    return _curses_panel_panel_show_impl(self, cls);
 }
 
 PyDoc_STRVAR(_curses_panel_panel_top__doc__,
@@ -106,18 +85,11 @@ _curses_panel_panel_top_impl(PyCursesPanelObject *self, PyTypeObject *cls);
 static PyObject *
 _curses_panel_panel_top(PyCursesPanelObject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":top", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "top() takes no arguments");
+        return NULL;
     }
-    return_value = _curses_panel_panel_top_impl(self, cls);
-
-exit:
-    return return_value;
+    return _curses_panel_panel_top_impl(self, cls);
 }
 
 PyDoc_STRVAR(_curses_panel_panel_above__doc__,
@@ -192,12 +164,21 @@ _curses_panel_panel_move(PyCursesPanelObject *self, PyTypeObject *cls, PyObject
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", "", NULL};
-    static _PyArg_Parser _parser = {"ii:move", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "move", 0};
+    PyObject *argsbuf[2];
     int y;
     int x;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &y, &x)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 2, 2, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    y = _PyLong_AsInt(args[0]);
+    if (y == -1 && PyErr_Occurred()) {
+        goto exit;
+    }
+    x = _PyLong_AsInt(args[1]);
+    if (x == -1 && PyErr_Occurred()) {
         goto exit;
     }
     return_value = _curses_panel_panel_move_impl(self, cls, y, x);
@@ -243,13 +224,19 @@ _curses_panel_panel_replace(PyCursesPanelObject *self, PyTypeObject *cls, PyObje
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", NULL};
-    static _PyArg_Parser _parser = {"O!:replace", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "replace", 0};
+    PyObject *argsbuf[1];
     PyCursesWindowObject *win;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &PyCursesWindow_Type, &win)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    if (!PyObject_TypeCheck(args[0], &PyCursesWindow_Type)) {
+        _PyArg_BadArgument("replace", "argument 1", (&PyCursesWindow_Type)->tp_name, args[0]);
         goto exit;
     }
+    win = (PyCursesWindowObject *)args[0];
     return_value = _curses_panel_panel_replace_impl(self, cls, win);
 
 exit:
@@ -274,13 +261,15 @@ _curses_panel_panel_set_userptr(PyCursesPanelObject *self, PyTypeObject *cls, Py
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", NULL};
-    static _PyArg_Parser _parser = {"O:set_userptr", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "set_userptr", 0};
+    PyObject *argsbuf[1];
     PyObject *obj;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &obj)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    obj = args[0];
     return_value = _curses_panel_panel_set_userptr_impl(self, cls, obj);
 
 exit:
@@ -303,18 +292,11 @@ _curses_panel_panel_userptr_impl(PyCursesPanelObject *self,
 static PyObject *
 _curses_panel_panel_userptr(PyCursesPanelObject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":userptr", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "userptr() takes no arguments");
+        return NULL;
     }
-    return_value = _curses_panel_panel_userptr_impl(self, cls);
-
-exit:
-    return return_value;
+    return _curses_panel_panel_userptr_impl(self, cls);
 }
 
 PyDoc_STRVAR(_curses_panel_bottom_panel__doc__,
@@ -401,4 +383,4 @@ _curses_panel_update_panels(PyObject *module, PyObject *Py_UNUSED(ignored))
 {
     return _curses_panel_update_panels_impl(module);
 }
-/*[clinic end generated code: output=3081ef24e5560cb0 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=c552457e8067bb0a input=a9049054013a1b77]*/
diff --git a/Modules/clinic/_dbmmodule.c.h b/Modules/clinic/_dbmmodule.c.h
index af288c2586a10b..beb26f612026b8 100644
--- a/Modules/clinic/_dbmmodule.c.h
+++ b/Modules/clinic/_dbmmodule.c.h
@@ -35,18 +35,11 @@ _dbm_dbm_keys_impl(dbmobject *self, PyTypeObject *cls);
 static PyObject *
 _dbm_dbm_keys(dbmobject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":keys", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "keys() takes no arguments");
+        return NULL;
     }
-    return_value = _dbm_dbm_keys_impl(self, cls);
-
-exit:
-    return return_value;
+    return _dbm_dbm_keys_impl(self, cls);
 }
 
 PyDoc_STRVAR(_dbm_dbm_get__doc__,
@@ -187,4 +180,4 @@ dbmopen(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=6947b1115df66f7c input=a9049054013a1b77]*/
+/*[clinic end generated code: output=a4599b89ce338b08 input=a9049054013a1b77]*/
diff --git a/Modules/clinic/_gdbmmodule.c.h b/Modules/clinic/_gdbmmodule.c.h
index ea4ee7df001c18..630cb499ae14fe 100644
--- a/Modules/clinic/_gdbmmodule.c.h
+++ b/Modules/clinic/_gdbmmodule.c.h
@@ -104,18 +104,11 @@ _gdbm_gdbm_keys_impl(gdbmobject *self, PyTypeObject *cls);
 static PyObject *
 _gdbm_gdbm_keys(gdbmobject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":keys", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "keys() takes no arguments");
+        return NULL;
     }
-    return_value = _gdbm_gdbm_keys_impl(self, cls);
-
-exit:
-    return return_value;
+    return _gdbm_gdbm_keys_impl(self, cls);
 }
 
 PyDoc_STRVAR(_gdbm_gdbm_firstkey__doc__,
@@ -137,18 +130,11 @@ _gdbm_gdbm_firstkey_impl(gdbmobject *self, PyTypeObject *cls);
 static PyObject *
 _gdbm_gdbm_firstkey(gdbmobject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":firstkey", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "firstkey() takes no arguments");
+        return NULL;
     }
-    return_value = _gdbm_gdbm_firstkey_impl(self, cls);
-
-exit:
-    return return_value;
+    return _gdbm_gdbm_firstkey_impl(self, cls);
 }
 
 PyDoc_STRVAR(_gdbm_gdbm_nextkey__doc__,
@@ -212,18 +198,11 @@ _gdbm_gdbm_reorganize_impl(gdbmobject *self, PyTypeObject *cls);
 static PyObject *
 _gdbm_gdbm_reorganize(gdbmobject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":reorganize", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "reorganize() takes no arguments");
+        return NULL;
     }
-    return_value = _gdbm_gdbm_reorganize_impl(self, cls);
-
-exit:
-    return return_value;
+    return _gdbm_gdbm_reorganize_impl(self, cls);
 }
 
 PyDoc_STRVAR(_gdbm_gdbm_sync__doc__,
@@ -244,18 +223,11 @@ _gdbm_gdbm_sync_impl(gdbmobject *self, PyTypeObject *cls);
 static PyObject *
 _gdbm_gdbm_sync(gdbmobject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":sync", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "sync() takes no arguments");
+        return NULL;
     }
-    return_value = _gdbm_gdbm_sync_impl(self, cls);
-
-exit:
-    return return_value;
+    return _gdbm_gdbm_sync_impl(self, cls);
 }
 
 PyDoc_STRVAR(dbmopen__doc__,
@@ -340,4 +312,4 @@ dbmopen(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=3b88446433e43d96 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=125f5bc685304744 input=a9049054013a1b77]*/
diff --git a/Modules/clinic/_lsprof.c.h b/Modules/clinic/_lsprof.c.h
index 5d9c209eab8563..b0adb746974ab3 100644
--- a/Modules/clinic/_lsprof.c.h
+++ b/Modules/clinic/_lsprof.c.h
@@ -39,17 +39,10 @@ _lsprof_Profiler_getstats_impl(ProfilerObject *self, PyTypeObject *cls);
 static PyObject *
 _lsprof_Profiler_getstats(ProfilerObject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":getstats", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "getstats() takes no arguments");
+        return NULL;
     }
-    return_value = _lsprof_Profiler_getstats_impl(self, cls);
-
-exit:
-    return return_value;
+    return _lsprof_Profiler_getstats_impl(self, cls);
 }
-/*[clinic end generated code: output=b4727cfebecdd22d input=a9049054013a1b77]*/
+/*[clinic end generated code: output=57c7b6b0b8666429 input=a9049054013a1b77]*/
diff --git a/Modules/clinic/_queuemodule.c.h b/Modules/clinic/_queuemodule.c.h
index 8741f7d9aff881..29e4c60cfa7558 100644
--- a/Modules/clinic/_queuemodule.c.h
+++ b/Modules/clinic/_queuemodule.c.h
@@ -144,14 +144,30 @@ _queue_SimpleQueue_get(simplequeueobject *self, PyTypeObject *cls, PyObject *con
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"block", "timeout", NULL};
-    static _PyArg_Parser _parser = {"|pO:get", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "get", 0};
+    PyObject *argsbuf[2];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 0;
     int block = 1;
     PyObject *timeout = Py_None;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &block, &timeout)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 0, 2, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    if (args[0]) {
+        block = PyObject_IsTrue(args[0]);
+        if (block < 0) {
+            goto exit;
+        }
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+    timeout = args[1];
+skip_optional_pos:
     return_value = _queue_SimpleQueue_get_impl(self, cls, block, timeout);
 
 exit:
@@ -177,18 +193,11 @@ _queue_SimpleQueue_get_nowait_impl(simplequeueobject *self,
 static PyObject *
 _queue_SimpleQueue_get_nowait(simplequeueobject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":get_nowait", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "get_nowait() takes no arguments");
+        return NULL;
     }
-    return_value = _queue_SimpleQueue_get_nowait_impl(self, cls);
-
-exit:
-    return return_value;
+    return _queue_SimpleQueue_get_nowait_impl(self, cls);
 }
 
 PyDoc_STRVAR(_queue_SimpleQueue_empty__doc__,
@@ -246,4 +255,4 @@ _queue_SimpleQueue_qsize(simplequeueobject *self, PyObject *Py_UNUSED(ignored))
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=ce56b46fac150909 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=a9d567e8a64e6170 input=a9049054013a1b77]*/
diff --git a/Modules/clinic/_sre.c.h b/Modules/clinic/_sre.c.h
index 72d772c289ae8b..d60827db24b065 100644
--- a/Modules/clinic/_sre.c.h
+++ b/Modules/clinic/_sre.c.h
@@ -176,15 +176,51 @@ _sre_SRE_Pattern_match(PatternObject *self, PyTypeObject *cls, PyObject *const *
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"string", "pos", "endpos", NULL};
-    static _PyArg_Parser _parser = {"O|nn:match", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "match", 0};
+    PyObject *argsbuf[3];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 1;
     PyObject *string;
     Py_ssize_t pos = 0;
     Py_ssize_t endpos = PY_SSIZE_T_MAX;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &string, &pos, &endpos)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 3, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    string = args[0];
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    if (args[1]) {
+        {
+            Py_ssize_t ival = -1;
+            PyObject *iobj = _PyNumber_Index(args[1]);
+            if (iobj != NULL) {
+                ival = PyLong_AsSsize_t(iobj);
+                Py_DECREF(iobj);
+            }
+            if (ival == -1 && PyErr_Occurred()) {
+                goto exit;
+            }
+            pos = ival;
+        }
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+    {
+        Py_ssize_t ival = -1;
+        PyObject *iobj = _PyNumber_Index(args[2]);
+        if (iobj != NULL) {
+            ival = PyLong_AsSsize_t(iobj);
+            Py_DECREF(iobj);
+        }
+        if (ival == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        endpos = ival;
+    }
+skip_optional_pos:
     return_value = _sre_SRE_Pattern_match_impl(self, cls, string, pos, endpos);
 
 exit:
@@ -210,15 +246,51 @@ _sre_SRE_Pattern_fullmatch(PatternObject *self, PyTypeObject *cls, PyObject *con
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"string", "pos", "endpos", NULL};
-    static _PyArg_Parser _parser = {"O|nn:fullmatch", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "fullmatch", 0};
+    PyObject *argsbuf[3];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 1;
     PyObject *string;
     Py_ssize_t pos = 0;
     Py_ssize_t endpos = PY_SSIZE_T_MAX;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &string, &pos, &endpos)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 3, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    string = args[0];
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    if (args[1]) {
+        {
+            Py_ssize_t ival = -1;
+            PyObject *iobj = _PyNumber_Index(args[1]);
+            if (iobj != NULL) {
+                ival = PyLong_AsSsize_t(iobj);
+                Py_DECREF(iobj);
+            }
+            if (ival == -1 && PyErr_Occurred()) {
+                goto exit;
+            }
+            pos = ival;
+        }
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+    {
+        Py_ssize_t ival = -1;
+        PyObject *iobj = _PyNumber_Index(args[2]);
+        if (iobj != NULL) {
+            ival = PyLong_AsSsize_t(iobj);
+            Py_DECREF(iobj);
+        }
+        if (ival == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        endpos = ival;
+    }
+skip_optional_pos:
     return_value = _sre_SRE_Pattern_fullmatch_impl(self, cls, string, pos, endpos);
 
 exit:
@@ -246,15 +318,51 @@ _sre_SRE_Pattern_search(PatternObject *self, PyTypeObject *cls, PyObject *const
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"string", "pos", "endpos", NULL};
-    static _PyArg_Parser _parser = {"O|nn:search", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "search", 0};
+    PyObject *argsbuf[3];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 1;
     PyObject *string;
     Py_ssize_t pos = 0;
     Py_ssize_t endpos = PY_SSIZE_T_MAX;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &string, &pos, &endpos)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 3, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    string = args[0];
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    if (args[1]) {
+        {
+            Py_ssize_t ival = -1;
+            PyObject *iobj = _PyNumber_Index(args[1]);
+            if (iobj != NULL) {
+                ival = PyLong_AsSsize_t(iobj);
+                Py_DECREF(iobj);
+            }
+            if (ival == -1 && PyErr_Occurred()) {
+                goto exit;
+            }
+            pos = ival;
+        }
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+    {
+        Py_ssize_t ival = -1;
+        PyObject *iobj = _PyNumber_Index(args[2]);
+        if (iobj != NULL) {
+            ival = PyLong_AsSsize_t(iobj);
+            Py_DECREF(iobj);
+        }
+        if (ival == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        endpos = ival;
+    }
+skip_optional_pos:
     return_value = _sre_SRE_Pattern_search_impl(self, cls, string, pos, endpos);
 
 exit:
@@ -351,15 +459,51 @@ _sre_SRE_Pattern_finditer(PatternObject *self, PyTypeObject *cls, PyObject *cons
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"string", "pos", "endpos", NULL};
-    static _PyArg_Parser _parser = {"O|nn:finditer", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "finditer", 0};
+    PyObject *argsbuf[3];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 1;
     PyObject *string;
     Py_ssize_t pos = 0;
     Py_ssize_t endpos = PY_SSIZE_T_MAX;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &string, &pos, &endpos)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 3, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    string = args[0];
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    if (args[1]) {
+        {
+            Py_ssize_t ival = -1;
+            PyObject *iobj = _PyNumber_Index(args[1]);
+            if (iobj != NULL) {
+                ival = PyLong_AsSsize_t(iobj);
+                Py_DECREF(iobj);
+            }
+            if (ival == -1 && PyErr_Occurred()) {
+                goto exit;
+            }
+            pos = ival;
+        }
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+    {
+        Py_ssize_t ival = -1;
+        PyObject *iobj = _PyNumber_Index(args[2]);
+        if (iobj != NULL) {
+            ival = PyLong_AsSsize_t(iobj);
+            Py_DECREF(iobj);
+        }
+        if (ival == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        endpos = ival;
+    }
+skip_optional_pos:
     return_value = _sre_SRE_Pattern_finditer_impl(self, cls, string, pos, endpos);
 
 exit:
@@ -384,15 +528,51 @@ _sre_SRE_Pattern_scanner(PatternObject *self, PyTypeObject *cls, PyObject *const
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"string", "pos", "endpos", NULL};
-    static _PyArg_Parser _parser = {"O|nn:scanner", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "scanner", 0};
+    PyObject *argsbuf[3];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 1;
     PyObject *string;
     Py_ssize_t pos = 0;
     Py_ssize_t endpos = PY_SSIZE_T_MAX;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &string, &pos, &endpos)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 3, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    string = args[0];
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    if (args[1]) {
+        {
+            Py_ssize_t ival = -1;
+            PyObject *iobj = _PyNumber_Index(args[1]);
+            if (iobj != NULL) {
+                ival = PyLong_AsSsize_t(iobj);
+                Py_DECREF(iobj);
+            }
+            if (ival == -1 && PyErr_Occurred()) {
+                goto exit;
+            }
+            pos = ival;
+        }
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+    {
+        Py_ssize_t ival = -1;
+        PyObject *iobj = _PyNumber_Index(args[2]);
+        if (iobj != NULL) {
+            ival = PyLong_AsSsize_t(iobj);
+            Py_DECREF(iobj);
+        }
+        if (ival == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        endpos = ival;
+    }
+skip_optional_pos:
     return_value = _sre_SRE_Pattern_scanner_impl(self, cls, string, pos, endpos);
 
 exit:
@@ -468,15 +648,35 @@ _sre_SRE_Pattern_sub(PatternObject *self, PyTypeObject *cls, PyObject *const *ar
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"repl", "string", "count", NULL};
-    static _PyArg_Parser _parser = {"OO|n:sub", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "sub", 0};
+    PyObject *argsbuf[3];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 2;
     PyObject *repl;
     PyObject *string;
     Py_ssize_t count = 0;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &repl, &string, &count)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 2, 3, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    repl = args[0];
+    string = args[1];
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    {
+        Py_ssize_t ival = -1;
+        PyObject *iobj = _PyNumber_Index(args[2]);
+        if (iobj != NULL) {
+            ival = PyLong_AsSsize_t(iobj);
+            Py_DECREF(iobj);
+        }
+        if (ival == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        count = ival;
+    }
+skip_optional_pos:
     return_value = _sre_SRE_Pattern_sub_impl(self, cls, repl, string, count);
 
 exit:
@@ -502,15 +702,35 @@ _sre_SRE_Pattern_subn(PatternObject *self, PyTypeObject *cls, PyObject *const *a
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"repl", "string", "count", NULL};
-    static _PyArg_Parser _parser = {"OO|n:subn", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "subn", 0};
+    PyObject *argsbuf[3];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 2;
     PyObject *repl;
     PyObject *string;
     Py_ssize_t count = 0;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &repl, &string, &count)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 2, 3, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    repl = args[0];
+    string = args[1];
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    {
+        Py_ssize_t ival = -1;
+        PyObject *iobj = _PyNumber_Index(args[2]);
+        if (iobj != NULL) {
+            ival = PyLong_AsSsize_t(iobj);
+            Py_DECREF(iobj);
+        }
+        if (ival == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        count = ival;
+    }
+skip_optional_pos:
     return_value = _sre_SRE_Pattern_subn_impl(self, cls, repl, string, count);
 
 exit:
@@ -869,18 +1089,11 @@ _sre_SRE_Scanner_match_impl(ScannerObject *self, PyTypeObject *cls);
 static PyObject *
 _sre_SRE_Scanner_match(ScannerObject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":match", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "match() takes no arguments");
+        return NULL;
     }
-    return_value = _sre_SRE_Scanner_match_impl(self, cls);
-
-exit:
-    return return_value;
+    return _sre_SRE_Scanner_match_impl(self, cls);
 }
 
 PyDoc_STRVAR(_sre_SRE_Scanner_search__doc__,
@@ -897,17 +1110,10 @@ _sre_SRE_Scanner_search_impl(ScannerObject *self, PyTypeObject *cls);
 static PyObject *
 _sre_SRE_Scanner_search(ScannerObject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":search", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "search() takes no arguments");
+        return NULL;
     }
-    return_value = _sre_SRE_Scanner_search_impl(self, cls);
-
-exit:
-    return return_value;
+    return _sre_SRE_Scanner_search_impl(self, cls);
 }
-/*[clinic end generated code: output=518f7bb775c1184f input=a9049054013a1b77]*/
+/*[clinic end generated code: output=ead5eb818b7771f8 input=a9049054013a1b77]*/
diff --git a/Modules/clinic/_testmultiphase.c.h b/Modules/clinic/_testmultiphase.c.h
index 17c28d54ce575a..26212d86dd0f87 100644
--- a/Modules/clinic/_testmultiphase.c.h
+++ b/Modules/clinic/_testmultiphase.c.h
@@ -21,18 +21,11 @@ _testmultiphase_StateAccessType_get_defining_module_impl(StateAccessTypeObject *
 static PyObject *
 _testmultiphase_StateAccessType_get_defining_module(StateAccessTypeObject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":get_defining_module", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "get_defining_module() takes no arguments");
+        return NULL;
     }
-    return_value = _testmultiphase_StateAccessType_get_defining_module_impl(self, cls);
-
-exit:
-    return return_value;
+    return _testmultiphase_StateAccessType_get_defining_module_impl(self, cls);
 }
 
 PyDoc_STRVAR(_testmultiphase_StateAccessType_getmodulebydef_bad_def__doc__,
@@ -51,18 +44,11 @@ _testmultiphase_StateAccessType_getmodulebydef_bad_def_impl(StateAccessTypeObjec
 static PyObject *
 _testmultiphase_StateAccessType_getmodulebydef_bad_def(StateAccessTypeObject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":getmodulebydef_bad_def", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "getmodulebydef_bad_def() takes no arguments");
+        return NULL;
     }
-    return_value = _testmultiphase_StateAccessType_getmodulebydef_bad_def_impl(self, cls);
-
-exit:
-    return return_value;
+    return _testmultiphase_StateAccessType_getmodulebydef_bad_def_impl(self, cls);
 }
 
 PyDoc_STRVAR(_testmultiphase_StateAccessType_increment_count_clinic__doc__,
@@ -88,14 +74,37 @@ _testmultiphase_StateAccessType_increment_count_clinic(StateAccessTypeObject *se
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"n", "twice", NULL};
-    static _PyArg_Parser _parser = {"|i$p:increment_count_clinic", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "increment_count_clinic", 0};
+    PyObject *argsbuf[2];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 0;
     int n = 1;
     int twice = 0;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &n, &twice)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 0, 1, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    if (args[0]) {
+        n = _PyLong_AsInt(args[0]);
+        if (n == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        if (!--noptargs) {
+            goto skip_optional_pos;
+        }
+    }
+skip_optional_pos:
+    if (!noptargs) {
+        goto skip_optional_kwonly;
+    }
+    twice = PyObject_IsTrue(args[1]);
+    if (twice < 0) {
+        goto exit;
+    }
+skip_optional_kwonly:
     return_value = _testmultiphase_StateAccessType_increment_count_clinic_impl(self, cls, n, twice);
 
 exit:
@@ -118,17 +127,10 @@ _testmultiphase_StateAccessType_get_count_impl(StateAccessTypeObject *self,
 static PyObject *
 _testmultiphase_StateAccessType_get_count(StateAccessTypeObject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":get_count", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "get_count() takes no arguments");
+        return NULL;
     }
-    return_value = _testmultiphase_StateAccessType_get_count_impl(self, cls);
-
-exit:
-    return return_value;
+    return _testmultiphase_StateAccessType_get_count_impl(self, cls);
 }
-/*[clinic end generated code: output=eb1b8c2ee6290be3 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=ec5029d1275cbf94 input=a9049054013a1b77]*/
diff --git a/Modules/clinic/arraymodule.c.h b/Modules/clinic/arraymodule.c.h
index c46cc738de91b7..ce98e411f0fe40 100644
--- a/Modules/clinic/arraymodule.c.h
+++ b/Modules/clinic/arraymodule.c.h
@@ -155,13 +155,15 @@ array_array_extend(arrayobject *self, PyTypeObject *cls, PyObject *const *args,
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", NULL};
-    static _PyArg_Parser _parser = {"O:extend", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "extend", 0};
+    PyObject *argsbuf[1];
     PyObject *bb;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &bb)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    bb = args[0];
     return_value = array_array_extend_impl(self, cls, bb);
 
 exit:
@@ -572,4 +574,4 @@ PyDoc_STRVAR(array_arrayiterator___setstate____doc__,
 
 #define ARRAY_ARRAYITERATOR___SETSTATE___METHODDEF    \
     {"__setstate__", (PyCFunction)array_arrayiterator___setstate__, METH_O, array_arrayiterator___setstate____doc__},
-/*[clinic end generated code: output=f130a994f98f1227 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=eb727e087d64f017 input=a9049054013a1b77]*/
diff --git a/Modules/clinic/md5module.c.h b/Modules/clinic/md5module.c.h
index 4762f2800d4b82..0ff09b0050a562 100644
--- a/Modules/clinic/md5module.c.h
+++ b/Modules/clinic/md5module.c.h
@@ -17,18 +17,11 @@ MD5Type_copy_impl(MD5object *self, PyTypeObject *cls);
 static PyObject *
 MD5Type_copy(MD5object *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":copy", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "copy() takes no arguments");
+        return NULL;
     }
-    return_value = MD5Type_copy_impl(self, cls);
-
-exit:
-    return return_value;
+    return MD5Type_copy_impl(self, cls);
 }
 
 PyDoc_STRVAR(MD5Type_digest__doc__,
@@ -126,4 +119,4 @@ _md5_md5(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *kw
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=53ff7f22dbaaea36 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=3061297a669c645c input=a9049054013a1b77]*/
diff --git a/Modules/clinic/posixmodule.c.h b/Modules/clinic/posixmodule.c.h
index 7921c222b90091..742acb8e6c07e3 100644
--- a/Modules/clinic/posixmodule.c.h
+++ b/Modules/clinic/posixmodule.c.h
@@ -8254,12 +8254,10 @@ static PyObject *
 os_DirEntry_is_symlink(DirEntry *self, PyTypeObject *defining_class, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
     PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":is_symlink", _keywords, 0};
     int _return_value;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "is_symlink() takes no arguments");
         goto exit;
     }
     _return_value = os_DirEntry_is_symlink_impl(self, defining_class);
@@ -8290,13 +8288,23 @@ os_DirEntry_stat(DirEntry *self, PyTypeObject *defining_class, PyObject *const *
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"follow_symlinks", NULL};
-    static _PyArg_Parser _parser = {"|$p:stat", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "stat", 0};
+    PyObject *argsbuf[1];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 0;
     int follow_symlinks = 1;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &follow_symlinks)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 0, 0, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    if (!noptargs) {
+        goto skip_optional_kwonly;
+    }
+    follow_symlinks = PyObject_IsTrue(args[0]);
+    if (follow_symlinks < 0) {
+        goto exit;
+    }
+skip_optional_kwonly:
     return_value = os_DirEntry_stat_impl(self, defining_class, follow_symlinks);
 
 exit:
@@ -8321,14 +8329,24 @@ os_DirEntry_is_dir(DirEntry *self, PyTypeObject *defining_class, PyObject *const
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"follow_symlinks", NULL};
-    static _PyArg_Parser _parser = {"|$p:is_dir", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "is_dir", 0};
+    PyObject *argsbuf[1];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 0;
     int follow_symlinks = 1;
     int _return_value;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &follow_symlinks)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 0, 0, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    if (!noptargs) {
+        goto skip_optional_kwonly;
+    }
+    follow_symlinks = PyObject_IsTrue(args[0]);
+    if (follow_symlinks < 0) {
+        goto exit;
+    }
+skip_optional_kwonly:
     _return_value = os_DirEntry_is_dir_impl(self, defining_class, follow_symlinks);
     if ((_return_value == -1) && PyErr_Occurred()) {
         goto exit;
@@ -8357,14 +8375,24 @@ os_DirEntry_is_file(DirEntry *self, PyTypeObject *defining_class, PyObject *cons
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"follow_symlinks", NULL};
-    static _PyArg_Parser _parser = {"|$p:is_file", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "is_file", 0};
+    PyObject *argsbuf[1];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 0;
     int follow_symlinks = 1;
     int _return_value;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &follow_symlinks)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 0, 0, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    if (!noptargs) {
+        goto skip_optional_kwonly;
+    }
+    follow_symlinks = PyObject_IsTrue(args[0]);
+    if (follow_symlinks < 0) {
+        goto exit;
+    }
+skip_optional_kwonly:
     _return_value = os_DirEntry_is_file_impl(self, defining_class, follow_symlinks);
     if ((_return_value == -1) && PyErr_Occurred()) {
         goto exit;
@@ -9263,4 +9291,4 @@ os_waitstatus_to_exitcode(PyObject *module, PyObject *const *args, Py_ssize_t na
 #ifndef OS_WAITSTATUS_TO_EXITCODE_METHODDEF
     #define OS_WAITSTATUS_TO_EXITCODE_METHODDEF
 #endif /* !defined(OS_WAITSTATUS_TO_EXITCODE_METHODDEF) */
-/*[clinic end generated code: output=65a85d7d3f2c487e input=a9049054013a1b77]*/
+/*[clinic end generated code: output=debefcf43738ec66 input=a9049054013a1b77]*/
diff --git a/Modules/clinic/pyexpat.c.h b/Modules/clinic/pyexpat.c.h
index 7c56d6a8b25910..bee2ee66950a5a 100644
--- a/Modules/clinic/pyexpat.c.h
+++ b/Modules/clinic/pyexpat.c.h
@@ -22,14 +22,24 @@ pyexpat_xmlparser_Parse(xmlparseobject *self, PyTypeObject *cls, PyObject *const
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", "", NULL};
-    static _PyArg_Parser _parser = {"O|i:Parse", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "Parse", 0};
+    PyObject *argsbuf[2];
     PyObject *data;
     int isfinal = 0;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &data, &isfinal)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 2, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    data = args[0];
+    if (nargs < 2) {
+        goto skip_optional_posonly;
+    }
+    isfinal = _PyLong_AsInt(args[1]);
+    if (isfinal == -1 && PyErr_Occurred()) {
         goto exit;
     }
+skip_optional_posonly:
     return_value = pyexpat_xmlparser_Parse_impl(self, cls, data, isfinal);
 
 exit:
@@ -54,13 +64,15 @@ pyexpat_xmlparser_ParseFile(xmlparseobject *self, PyTypeObject *cls, PyObject *c
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", NULL};
-    static _PyArg_Parser _parser = {"O:ParseFile", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "ParseFile", 0};
+    PyObject *argsbuf[1];
     PyObject *file;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &file)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    file = args[0];
     return_value = pyexpat_xmlparser_ParseFile_impl(self, cls, file);
 
 exit:
@@ -164,14 +176,50 @@ pyexpat_xmlparser_ExternalEntityParserCreate(xmlparseobject *self, PyTypeObject
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", "", NULL};
-    static _PyArg_Parser _parser = {"z|s:ExternalEntityParserCreate", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "ExternalEntityParserCreate", 0};
+    PyObject *argsbuf[2];
     const char *context;
     const char *encoding = NULL;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &context, &encoding)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 2, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    if (args[0] == Py_None) {
+        context = NULL;
+    }
+    else if (PyUnicode_Check(args[0])) {
+        Py_ssize_t context_length;
+        context = PyUnicode_AsUTF8AndSize(args[0], &context_length);
+        if (context == NULL) {
+            goto exit;
+        }
+        if (strlen(context) != (size_t)context_length) {
+            PyErr_SetString(PyExc_ValueError, "embedded null character");
+            goto exit;
+        }
+    }
+    else {
+        _PyArg_BadArgument("ExternalEntityParserCreate", "argument 1", "str or None", args[0]);
+        goto exit;
+    }
+    if (nargs < 2) {
+        goto skip_optional_posonly;
+    }
+    if (!PyUnicode_Check(args[1])) {
+        _PyArg_BadArgument("ExternalEntityParserCreate", "argument 2", "str", args[1]);
         goto exit;
     }
+    Py_ssize_t encoding_length;
+    encoding = PyUnicode_AsUTF8AndSize(args[1], &encoding_length);
+    if (encoding == NULL) {
+        goto exit;
+    }
+    if (strlen(encoding) != (size_t)encoding_length) {
+        PyErr_SetString(PyExc_ValueError, "embedded null character");
+        goto exit;
+    }
+skip_optional_posonly:
     return_value = pyexpat_xmlparser_ExternalEntityParserCreate_impl(self, cls, context, encoding);
 
 exit:
@@ -235,13 +283,22 @@ pyexpat_xmlparser_UseForeignDTD(xmlparseobject *self, PyTypeObject *cls, PyObjec
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", NULL};
-    static _PyArg_Parser _parser = {"|p:UseForeignDTD", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "UseForeignDTD", 0};
+    PyObject *argsbuf[1];
     int flag = 1;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &flag)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 0, 1, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    if (nargs < 1) {
+        goto skip_optional_posonly;
+    }
+    flag = PyObject_IsTrue(args[0]);
+    if (flag < 0) {
         goto exit;
     }
+skip_optional_posonly:
     return_value = pyexpat_xmlparser_UseForeignDTD_impl(self, cls, flag);
 
 exit:
@@ -368,4 +425,4 @@ pyexpat_ErrorString(PyObject *module, PyObject *arg)
 #ifndef PYEXPAT_XMLPARSER_USEFOREIGNDTD_METHODDEF
     #define PYEXPAT_XMLPARSER_USEFOREIGNDTD_METHODDEF
 #endif /* !defined(PYEXPAT_XMLPARSER_USEFOREIGNDTD_METHODDEF) */
-/*[clinic end generated code: output=612b9d6a17a679a7 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=5d60049d385d5d56 input=a9049054013a1b77]*/
diff --git a/Modules/clinic/sha1module.c.h b/Modules/clinic/sha1module.c.h
index 3a3ab58c1233cf..d9a2e150f6d417 100644
--- a/Modules/clinic/sha1module.c.h
+++ b/Modules/clinic/sha1module.c.h
@@ -17,18 +17,11 @@ SHA1Type_copy_impl(SHA1object *self, PyTypeObject *cls);
 static PyObject *
 SHA1Type_copy(SHA1object *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":copy", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "copy() takes no arguments");
+        return NULL;
     }
-    return_value = SHA1Type_copy_impl(self, cls);
-
-exit:
-    return return_value;
+    return SHA1Type_copy_impl(self, cls);
 }
 
 PyDoc_STRVAR(SHA1Type_digest__doc__,
@@ -126,4 +119,4 @@ _sha1_sha1(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObject *
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=abf1ab2545cea5a2 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=93ced3c8f8fa4f21 input=a9049054013a1b77]*/
diff --git a/Modules/clinic/sha256module.c.h b/Modules/clinic/sha256module.c.h
index 89205c4f14f4e4..619fab1a6fe2fb 100644
--- a/Modules/clinic/sha256module.c.h
+++ b/Modules/clinic/sha256module.c.h
@@ -17,18 +17,11 @@ SHA256Type_copy_impl(SHAobject *self, PyTypeObject *cls);
 static PyObject *
 SHA256Type_copy(SHAobject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":copy", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "copy() takes no arguments");
+        return NULL;
     }
-    return_value = SHA256Type_copy_impl(self, cls);
-
-exit:
-    return return_value;
+    return SHA256Type_copy_impl(self, cls);
 }
 
 PyDoc_STRVAR(SHA256Type_digest__doc__,
@@ -177,4 +170,4 @@ _sha256_sha224(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObje
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=b7283f75c9d08f30 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=4f9fe3ca546b0c58 input=a9049054013a1b77]*/
diff --git a/Modules/clinic/sha512module.c.h b/Modules/clinic/sha512module.c.h
index f1192d74f9a1ab..fada35eff22614 100644
--- a/Modules/clinic/sha512module.c.h
+++ b/Modules/clinic/sha512module.c.h
@@ -17,18 +17,11 @@ SHA512Type_copy_impl(SHAobject *self, PyTypeObject *cls);
 static PyObject *
 SHA512Type_copy(SHAobject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":copy", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "copy() takes no arguments");
+        return NULL;
     }
-    return_value = SHA512Type_copy_impl(self, cls);
-
-exit:
-    return return_value;
+    return SHA512Type_copy_impl(self, cls);
 }
 
 PyDoc_STRVAR(SHA512Type_digest__doc__,
@@ -177,4 +170,4 @@ _sha512_sha384(PyObject *module, PyObject *const *args, Py_ssize_t nargs, PyObje
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=9ff9f11937fabf35 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=26d2fe27b9673ac2 input=a9049054013a1b77]*/
diff --git a/Modules/clinic/zlibmodule.c.h b/Modules/clinic/zlibmodule.c.h
index 14e955db64e729..43948398590632 100644
--- a/Modules/clinic/zlibmodule.c.h
+++ b/Modules/clinic/zlibmodule.c.h
@@ -340,11 +340,19 @@ zlib_Compress_compress(compobject *self, PyTypeObject *cls, PyObject *const *arg
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", NULL};
-    static _PyArg_Parser _parser = {"y*:compress", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "compress", 0};
+    PyObject *argsbuf[1];
     Py_buffer data = {NULL, NULL};
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &data)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    if (PyObject_GetBuffer(args[0], &data, PyBUF_SIMPLE) != 0) {
+        goto exit;
+    }
+    if (!PyBuffer_IsContiguous(&data, 'C')) {
+        _PyArg_BadArgument("compress", "argument 1", "contiguous buffer", args[0]);
         goto exit;
     }
     return_value = zlib_Compress_compress_impl(self, cls, &data);
@@ -387,14 +395,39 @@ zlib_Decompress_decompress(compobject *self, PyTypeObject *cls, PyObject *const
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", "max_length", NULL};
-    static _PyArg_Parser _parser = {"y*|n:decompress", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "decompress", 0};
+    PyObject *argsbuf[2];
+    Py_ssize_t noptargs = nargs + (kwnames ? PyTuple_GET_SIZE(kwnames) : 0) - 1;
     Py_buffer data = {NULL, NULL};
     Py_ssize_t max_length = 0;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &data, &max_length)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 2, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    if (PyObject_GetBuffer(args[0], &data, PyBUF_SIMPLE) != 0) {
         goto exit;
     }
+    if (!PyBuffer_IsContiguous(&data, 'C')) {
+        _PyArg_BadArgument("decompress", "argument 1", "contiguous buffer", args[0]);
+        goto exit;
+    }
+    if (!noptargs) {
+        goto skip_optional_pos;
+    }
+    {
+        Py_ssize_t ival = -1;
+        PyObject *iobj = _PyNumber_Index(args[1]);
+        if (iobj != NULL) {
+            ival = PyLong_AsSsize_t(iobj);
+            Py_DECREF(iobj);
+        }
+        if (ival == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        max_length = ival;
+    }
+skip_optional_pos:
     return_value = zlib_Decompress_decompress_impl(self, cls, &data, max_length);
 
 exit:
@@ -429,13 +462,22 @@ zlib_Compress_flush(compobject *self, PyTypeObject *cls, PyObject *const *args,
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", NULL};
-    static _PyArg_Parser _parser = {"|i:flush", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "flush", 0};
+    PyObject *argsbuf[1];
     int mode = Z_FINISH;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &mode)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 0, 1, 0, argsbuf);
+    if (!args) {
+        goto exit;
+    }
+    if (nargs < 1) {
+        goto skip_optional_posonly;
+    }
+    mode = _PyLong_AsInt(args[0]);
+    if (mode == -1 && PyErr_Occurred()) {
         goto exit;
     }
+skip_optional_posonly:
     return_value = zlib_Compress_flush_impl(self, cls, mode);
 
 exit:
@@ -459,18 +501,11 @@ zlib_Compress_copy_impl(compobject *self, PyTypeObject *cls);
 static PyObject *
 zlib_Compress_copy(compobject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":copy", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "copy() takes no arguments");
+        return NULL;
     }
-    return_value = zlib_Compress_copy_impl(self, cls);
-
-exit:
-    return return_value;
+    return zlib_Compress_copy_impl(self, cls);
 }
 
 #endif /* defined(HAVE_ZLIB_COPY) */
@@ -491,18 +526,11 @@ zlib_Compress___copy___impl(compobject *self, PyTypeObject *cls);
 static PyObject *
 zlib_Compress___copy__(compobject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":__copy__", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "__copy__() takes no arguments");
+        return NULL;
     }
-    return_value = zlib_Compress___copy___impl(self, cls);
-
-exit:
-    return return_value;
+    return zlib_Compress___copy___impl(self, cls);
 }
 
 #endif /* defined(HAVE_ZLIB_COPY) */
@@ -526,13 +554,15 @@ zlib_Compress___deepcopy__(compobject *self, PyTypeObject *cls, PyObject *const
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", NULL};
-    static _PyArg_Parser _parser = {"O:__deepcopy__", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "__deepcopy__", 0};
+    PyObject *argsbuf[1];
     PyObject *memo;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &memo)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    memo = args[0];
     return_value = zlib_Compress___deepcopy___impl(self, cls, memo);
 
 exit:
@@ -558,18 +588,11 @@ zlib_Decompress_copy_impl(compobject *self, PyTypeObject *cls);
 static PyObject *
 zlib_Decompress_copy(compobject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":copy", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "copy() takes no arguments");
+        return NULL;
     }
-    return_value = zlib_Decompress_copy_impl(self, cls);
-
-exit:
-    return return_value;
+    return zlib_Decompress_copy_impl(self, cls);
 }
 
 #endif /* defined(HAVE_ZLIB_COPY) */
@@ -590,18 +613,11 @@ zlib_Decompress___copy___impl(compobject *self, PyTypeObject *cls);
 static PyObject *
 zlib_Decompress___copy__(compobject *self, PyTypeObject *cls, PyObject *const *args, Py_ssize_t nargs, PyObject *kwnames)
 {
-    PyObject *return_value = NULL;
-    static const char * const _keywords[] = { NULL};
-    static _PyArg_Parser _parser = {":__copy__", _keywords, 0};
-
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser
-        )) {
-        goto exit;
+    if (nargs) {
+        PyErr_SetString(PyExc_TypeError, "__copy__() takes no arguments");
+        return NULL;
     }
-    return_value = zlib_Decompress___copy___impl(self, cls);
-
-exit:
-    return return_value;
+    return zlib_Decompress___copy___impl(self, cls);
 }
 
 #endif /* defined(HAVE_ZLIB_COPY) */
@@ -625,13 +641,15 @@ zlib_Decompress___deepcopy__(compobject *self, PyTypeObject *cls, PyObject *cons
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", NULL};
-    static _PyArg_Parser _parser = {"O:__deepcopy__", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "__deepcopy__", 0};
+    PyObject *argsbuf[1];
     PyObject *memo;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &memo)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 1, 1, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    memo = args[0];
     return_value = zlib_Decompress___deepcopy___impl(self, cls, memo);
 
 exit:
@@ -661,13 +679,30 @@ zlib_Decompress_flush(compobject *self, PyTypeObject *cls, PyObject *const *args
 {
     PyObject *return_value = NULL;
     static const char * const _keywords[] = {"", NULL};
-    static _PyArg_Parser _parser = {"|n:flush", _keywords, 0};
+    static _PyArg_Parser _parser = {NULL, _keywords, "flush", 0};
+    PyObject *argsbuf[1];
     Py_ssize_t length = DEF_BUF_SIZE;
 
-    if (!_PyArg_ParseStackAndKeywords(args, nargs, kwnames, &_parser,
-        &length)) {
+    args = _PyArg_UnpackKeywords(args, nargs, NULL, kwnames, &_parser, 0, 1, 0, argsbuf);
+    if (!args) {
         goto exit;
     }
+    if (nargs < 1) {
+        goto skip_optional_posonly;
+    }
+    {
+        Py_ssize_t ival = -1;
+        PyObject *iobj = _PyNumber_Index(args[0]);
+        if (iobj != NULL) {
+            ival = PyLong_AsSsize_t(iobj);
+            Py_DECREF(iobj);
+        }
+        if (ival == -1 && PyErr_Occurred()) {
+            goto exit;
+        }
+        length = ival;
+    }
+skip_optional_posonly:
     return_value = zlib_Decompress_flush_impl(self, cls, length);
 
 exit:
@@ -803,4 +838,4 @@ zlib_crc32(PyObject *module, PyObject *const *args, Py_ssize_t nargs)
 #ifndef ZLIB_DECOMPRESS___DEEPCOPY___METHODDEF
     #define ZLIB_DECOMPRESS___DEEPCOPY___METHODDEF
 #endif /* !defined(ZLIB_DECOMPRESS___DEEPCOPY___METHODDEF) */
-/*[clinic end generated code: output=6736bae59fab268b input=a9049054013a1b77]*/
+/*[clinic end generated code: output=1bda0d996fb51269 input=a9049054013a1b77]*/
diff --git a/Tools/clinic/clinic.py b/Tools/clinic/clinic.py
index 969008ade9790f..b442c494d31d49 100755
--- a/Tools/clinic/clinic.py
+++ b/Tools/clinic/clinic.py
@@ -636,6 +636,10 @@ def output_templates(self, f):
         assert parameters
         assert isinstance(parameters[0].converter, self_converter)
         del parameters[0]
+        requires_defining_class = False
+        if parameters and isinstance(parameters[0].converter, defining_class_converter):
+            requires_defining_class = True
+            del parameters[0]
         converters = [p.converter for p in parameters]
 
         has_option_groups = parameters and (parameters[0].group or parameters[-1].group)
@@ -657,10 +661,6 @@ def output_templates(self, f):
                 if not p.is_optional():
                     min_pos = i
 
-        requires_defining_class = any(
-            isinstance(p.converter, defining_class_converter)
-            for p in parameters)
-
         meth_o = (len(parameters) == 1 and
               parameters[0].is_positional_only() and
               not converters[0].is_optional() and
@@ -763,24 +763,40 @@ def parser_body(prototype, *fields, declarations=''):
             return linear_format(output(), parser_declarations=declarations)
 
         if not parameters:
-            # no parameters, METH_NOARGS
+            if not requires_defining_class:
+                # no parameters, METH_NOARGS
+                flags = "METH_NOARGS"
 
-            flags = "METH_NOARGS"
+                parser_prototype = normalize_snippet("""
+                    static PyObject *
+                    {c_basename}({self_type}{self_name}, PyObject *Py_UNUSED(ignored))
+                    """)
+                parser_code = []
 
-            parser_prototype = normalize_snippet("""
-                static PyObject *
-                {c_basename}({self_type}{self_name}, PyObject *Py_UNUSED(ignored))
-                """)
-            parser_definition = parser_prototype
+            else:
+                assert not new_or_init
 
-            if default_return_converter:
-                parser_definition = parser_prototype + '\n' + normalize_snippet("""
-                    {{
-                        return {c_basename}_impl({impl_arguments});
+                flags = "METH_METHOD|METH_FASTCALL|METH_KEYWORDS"
+
+                parser_prototype = parser_prototype_def_class
+                return_error = ('return NULL;' if default_return_converter
+                                else 'goto exit;')
+                parser_code = [normalize_snippet("""
+                    if (nargs) {{
+                        PyErr_SetString(PyExc_TypeError, "{name}() takes no arguments");
+                        %s
                     }}
-                    """)
+                    """ % return_error, indent=4)]
+
+            if default_return_converter:
+                parser_definition = '\n'.join([
+                    parser_prototype,
+                    '{{',
+                    *parser_code,
+                    '    return {c_basename}_impl({impl_arguments});',
+                    '}}'])
             else:
-                parser_definition = parser_body(parser_prototype)
+                parser_definition = parser_body(parser_prototype, *parser_code)
 
         elif meth_o:
             flags = "METH_O"
@@ -939,6 +955,9 @@ def parser_body(prototype, *fields, declarations=''):
 
             add_label = None
             for i, p in enumerate(parameters):
+                if isinstance(p.converter, defining_class_converter):
+                    raise ValueError("defining_class should be the first "
+                                     "parameter (after self)")
                 displayname = p.get_displayname(i+1)
                 parsearg = p.converter.parse_arg(argname_fmt % i, displayname)
                 if parsearg is None: