bpo-43413: Fix handling keyword arguments in subclasses of some buitin classes (GH-26456)

* Constructors of subclasses of some buitin classes (e.g. tuple, list,
  frozenset) no longer accept arbitrary keyword arguments.
* Subclass of set can now define a __new__() method with additional
  keyword parameters without overriding also __init__().

Author: serhiy-storchaka

Lib/test/seq_tests.py

@@ -145,6 +145,9 @@ def __getitem__(self, i):
         self.assertEqual(self.type2test(LyingTuple((2,))), self.type2test((1,)))
         self.assertEqual(self.type2test(LyingList([2])), self.type2test([1]))
 
+        with self.assertRaises(TypeError):
+            self.type2test(unsupported_arg=[])
+
     def test_truth(self):
         self.assertFalse(self.type2test())
         self.assertTrue(self.type2test([42]))

Lib/test/test_float.py

@@ -245,6 +245,33 @@ def test_keyword_args(self):
         with self.assertRaisesRegex(TypeError, 'keyword argument'):
             float(x='3.14')
 
+    def test_keywords_in_subclass(self):
+        class subclass(float):
+            pass
+        u = subclass(2.5)
+        self.assertIs(type(u), subclass)
+        self.assertEqual(float(u), 2.5)
+        with self.assertRaises(TypeError):
+            subclass(x=0)
+
+        class subclass_with_init(float):
+            def __init__(self, arg, newarg=None):
+                self.newarg = newarg
+        u = subclass_with_init(2.5, newarg=3)
+        self.assertIs(type(u), subclass_with_init)
+        self.assertEqual(float(u), 2.5)
+        self.assertEqual(u.newarg, 3)
+
+        class subclass_with_new(float):
+            def __new__(cls, arg, newarg=None):
+                self = super().__new__(cls, arg)
+                self.newarg = newarg
+                return self
+        u = subclass_with_new(2.5, newarg=3)
+        self.assertIs(type(u), subclass_with_new)
+        self.assertEqual(float(u), 2.5)
+        self.assertEqual(u.newarg, 3)
+
     def test_is_integer(self):
         self.assertFalse((1.1).is_integer())
         self.assertTrue((1.).is_integer())

Lib/test/test_itertools.py

@@ -2229,16 +2229,57 @@ def __eq__(self, other):
 class SubclassWithKwargsTest(unittest.TestCase):
     def test_keywords_in_subclass(self):
         # count is not subclassable...
-        for cls in (repeat, zip, filter, filterfalse, chain, map,
-                    starmap, islice, takewhile, dropwhile, cycle, compress):
-            class Subclass(cls):
-                def __init__(self, newarg=None, *args):
-                    cls.__init__(self, *args)
-            try:
-                Subclass(newarg=1)
-            except TypeError as err:
-                # we expect type errors because of wrong argument count
-                self.assertNotIn("keyword arguments", err.args[0])
+        testcases = [
+            (repeat, (1, 2), [1, 1]),
+            (zip, ([1, 2], 'ab'), [(1, 'a'), (2, 'b')]),
+            (filter, (None, [0, 1]), [1]),
+            (filterfalse, (None, [0, 1]), [0]),
+            (chain, ([1, 2], [3, 4]), [1, 2, 3]),
+            (map, (str, [1, 2]), ['1', '2']),
+            (starmap, (operator.pow, ((2, 3), (3, 2))), [8, 9]),
+            (islice, ([1, 2, 3, 4], 1, 3), [2, 3]),
+            (takewhile, (isEven, [2, 3, 4]), [2]),
+            (dropwhile, (isEven, [2, 3, 4]), [3, 4]),
+            (cycle, ([1, 2],), [1, 2, 1]),
+            (compress, ('ABC', [1, 0, 1]), ['A', 'C']),
+        ]
+        for cls, args, result in testcases:
+            with self.subTest(cls):
+                class subclass(cls):
+                    pass
+                u = subclass(*args)
+                self.assertIs(type(u), subclass)
+                self.assertEqual(list(islice(u, 0, 3)), result)
+                with self.assertRaises(TypeError):
+                    subclass(*args, newarg=3)
+
+        for cls, args, result in testcases:
+            # Constructors of repeat, zip, compress accept keyword arguments.
+            # Their subclasses need overriding __new__ to support new
+            # keyword arguments.
+            if cls in [repeat, zip, compress]:
+                continue
+            with self.subTest(cls):
+                class subclass_with_init(cls):
+                    def __init__(self, *args, newarg=None):
+                        self.newarg = newarg
+                u = subclass_with_init(*args, newarg=3)
+                self.assertIs(type(u), subclass_with_init)
+                self.assertEqual(list(islice(u, 0, 3)), result)
+                self.assertEqual(u.newarg, 3)
+
+        for cls, args, result in testcases:
+            with self.subTest(cls):
+                class subclass_with_new(cls):
+                    def __new__(cls, *args, newarg=None):
+                        self = super().__new__(cls, *args)
+                        self.newarg = newarg
+                        return self
+                u = subclass_with_new(*args, newarg=3)
+                self.assertIs(type(u), subclass_with_new)
+                self.assertEqual(list(islice(u, 0, 3)), result)
+                self.assertEqual(u.newarg, 3)
+
 
 @support.cpython_only
 class SizeofTest(unittest.TestCase):

Lib/test/test_list.py

@@ -46,6 +46,34 @@ def test_keyword_args(self):
         with self.assertRaisesRegex(TypeError, 'keyword argument'):
             list(sequence=[])
 
+    def test_keywords_in_subclass(self):
+        class subclass(list):
+            pass
+        u = subclass([1, 2])
+        self.assertIs(type(u), subclass)
+        self.assertEqual(list(u), [1, 2])
+        with self.assertRaises(TypeError):
+            subclass(sequence=())
+
+        class subclass_with_init(list):
+            def __init__(self, seq, newarg=None):
+                super().__init__(seq)
+                self.newarg = newarg
+        u = subclass_with_init([1, 2], newarg=3)
+        self.assertIs(type(u), subclass_with_init)
+        self.assertEqual(list(u), [1, 2])
+        self.assertEqual(u.newarg, 3)
+
+        class subclass_with_new(list):
+            def __new__(cls, seq, newarg=None):
+                self = super().__new__(cls, seq)
+                self.newarg = newarg
+                return self
+        u = subclass_with_new([1, 2], newarg=3)
+        self.assertIs(type(u), subclass_with_new)
+        self.assertEqual(list(u), [1, 2])
+        self.assertEqual(u.newarg, 3)
+
     def test_truth(self):
         super().test_truth()
         self.assertTrue(not [])

Lib/test/test_set.py

@@ -644,15 +644,34 @@ class TestSetSubclass(TestSet):
     thetype = SetSubclass
     basetype = set
 
-class SetSubclassWithKeywordArgs(set):
-    def __init__(self, iterable=[], newarg=None):
-        set.__init__(self, iterable)
-
-class TestSetSubclassWithKeywordArgs(TestSet):
-
     def test_keywords_in_subclass(self):
-        'SF bug #1486663 -- this used to erroneously raise a TypeError'
-        SetSubclassWithKeywordArgs(newarg=1)
+        class subclass(set):
+            pass
+        u = subclass([1, 2])
+        self.assertIs(type(u), subclass)
+        self.assertEqual(set(u), {1, 2})
+        with self.assertRaises(TypeError):
+            subclass(sequence=())
+
+        class subclass_with_init(set):
+            def __init__(self, arg, newarg=None):
+                super().__init__(arg)
+                self.newarg = newarg
+        u = subclass_with_init([1, 2], newarg=3)
+        self.assertIs(type(u), subclass_with_init)
+        self.assertEqual(set(u), {1, 2})
+        self.assertEqual(u.newarg, 3)
+
+        class subclass_with_new(set):
+            def __new__(cls, arg, newarg=None):
+                self = super().__new__(cls, arg)
+                self.newarg = newarg
+                return self
+        u = subclass_with_new([1, 2], newarg=3)
+        self.assertIs(type(u), subclass_with_new)
+        self.assertEqual(set(u), {1, 2})
+        self.assertEqual(u.newarg, 3)
+
 
 class TestFrozenSet(TestJointOps, unittest.TestCase):
     thetype = frozenset
@@ -734,6 +753,33 @@ class TestFrozenSetSubclass(TestFrozenSet):
     thetype = FrozenSetSubclass
     basetype = frozenset
 
+    def test_keywords_in_subclass(self):
+        class subclass(frozenset):
+            pass
+        u = subclass([1, 2])
+        self.assertIs(type(u), subclass)
+        self.assertEqual(set(u), {1, 2})
+        with self.assertRaises(TypeError):
+            subclass(sequence=())
+
+        class subclass_with_init(frozenset):
+            def __init__(self, arg, newarg=None):
+                self.newarg = newarg
+        u = subclass_with_init([1, 2], newarg=3)
+        self.assertIs(type(u), subclass_with_init)
+        self.assertEqual(set(u), {1, 2})
+        self.assertEqual(u.newarg, 3)
+
+        class subclass_with_new(frozenset):
+            def __new__(cls, arg, newarg=None):
+                self = super().__new__(cls, arg)
+                self.newarg = newarg
+                return self
+        u = subclass_with_new([1, 2], newarg=3)
+        self.assertIs(type(u), subclass_with_new)
+        self.assertEqual(set(u), {1, 2})
+        self.assertEqual(u.newarg, 3)
+
     def test_constructor_identity(self):
         s = self.thetype(range(3))
         t = self.thetype(s)

Lib/test/test_tuple.py

@@ -42,6 +42,33 @@ def test_keyword_args(self):
         with self.assertRaisesRegex(TypeError, 'keyword argument'):
             tuple(sequence=())
 
+    def test_keywords_in_subclass(self):
+        class subclass(tuple):
+            pass
+        u = subclass([1, 2])
+        self.assertIs(type(u), subclass)
+        self.assertEqual(list(u), [1, 2])
+        with self.assertRaises(TypeError):
+            subclass(sequence=())
+
+        class subclass_with_init(tuple):
+            def __init__(self, arg, newarg=None):
+                self.newarg = newarg
+        u = subclass_with_init([1, 2], newarg=3)
+        self.assertIs(type(u), subclass_with_init)
+        self.assertEqual(list(u), [1, 2])
+        self.assertEqual(u.newarg, 3)
+
+        class subclass_with_new(tuple):
+            def __new__(cls, arg, newarg=None):
+                self = super().__new__(cls, arg)
+                self.newarg = newarg
+                return self
+        u = subclass_with_new([1, 2], newarg=3)
+        self.assertIs(type(u), subclass_with_new)
+        self.assertEqual(list(u), [1, 2])
+        self.assertEqual(u.newarg, 3)
+
     def test_truth(self):
         super().test_truth()
         self.assertTrue(not ())

Misc/NEWS.d/next/Core and Builtins/2021-05-30-16-37-47.bpo-43413.vYFPPC.rst

@@ -0,0 +1,4 @@
+Constructors of subclasses of some buitin classes (e.g. :class:`tuple`,
+:class:`list`, :class:`frozenset`) no longer accept arbitrary keyword
+arguments. Subclass of :class:`set` can now define a ``__new__()`` method
+with additional keyword parameters without overriding also ``__init__()``.

Modules/_io/clinic/bufferedio.c.h

@@ -553,7 +553,8 @@ _io_BufferedRWPair___init__(PyObject *self, PyObject *args, PyObject *kwargs)
     PyObject *writer;
     Py_ssize_t buffer_size = DEFAULT_BUFFER_SIZE;
 
-    if (Py_IS_TYPE(self, &PyBufferedRWPair_Type) &&
+    if ((Py_IS_TYPE(self, &PyBufferedRWPair_Type) ||
+         Py_TYPE(self)->tp_new == PyBufferedRWPair_Type.tp_new) &&
         !_PyArg_NoKeywords("BufferedRWPair", kwargs)) {
         goto exit;
     }
@@ -637,4 +638,4 @@ _io_BufferedRandom___init__(PyObject *self, PyObject *args, PyObject *kwargs)
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=98ccf7610c0e82ba input=a9049054013a1b77]*/
+/*[clinic end generated code: output=79138a088729b5ee input=a9049054013a1b77]*/

Modules/_randommodule.c

@@ -523,8 +523,9 @@ random_init(RandomObject *self, PyObject *args, PyObject *kwds)
     PyObject *arg = NULL;
     _randomstate *state = _randomstate_type(Py_TYPE(self));
 
-    if (Py_IS_TYPE(self, (PyTypeObject *)state->Random_Type) &&
-        !_PyArg_NoKeywords("Random()", kwds)) {
+    if ((Py_IS_TYPE(self, (PyTypeObject *)state->Random_Type) ||
+         Py_TYPE(self)->tp_init == ((PyTypeObject*)state->Random_Type)->tp_init) &&
+        !_PyArg_NoKeywords("Random", kwds)) {
         return -1;
     }
 

Modules/_sqlite/clinic/cursor.c.h

@@ -12,7 +12,8 @@ pysqlite_cursor_init(PyObject *self, PyObject *args, PyObject *kwargs)
     int return_value = -1;
     pysqlite_Connection *connection;
 
-    if (Py_IS_TYPE(self, clinic_state()->CursorType) &&
+    if ((Py_IS_TYPE(self, clinic_state()->CursorType) ||
+         Py_TYPE(self)->tp_new == clinic_state()->CursorType->tp_new) &&
         !_PyArg_NoKeywords("Cursor", kwargs)) {
         goto exit;
     }
@@ -299,4 +300,4 @@ pysqlite_cursor_close(pysqlite_Cursor *self, PyTypeObject *cls, PyObject *const
 exit:
     return return_value;
 }
-/*[clinic end generated code: output=ace31a7481aa3f41 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=3b5328c1619b7626 input=a9049054013a1b77]*/

Modules/_sqlite/clinic/row.c.h

@@ -13,7 +13,8 @@ pysqlite_row_new(PyTypeObject *type, PyObject *args, PyObject *kwargs)
     pysqlite_Cursor *cursor;
     PyObject *data;
 
-    if ((type == clinic_state()->RowType) &&
+    if ((type == clinic_state()->RowType ||
+         type->tp_init == clinic_state()->RowType->tp_init) &&
         !_PyArg_NoKeywords("Row", kwargs)) {
         goto exit;
     }
@@ -53,4 +54,4 @@ pysqlite_row_keys(pysqlite_Row *self, PyObject *Py_UNUSED(ignored))
 {
     return pysqlite_row_keys_impl(self);
 }
-/*[clinic end generated code: output=0382771b4fc85f36 input=a9049054013a1b77]*/
+/*[clinic end generated code: output=9d54919dbb4ba5f1 input=a9049054013a1b77]*/

Modules/arraymodule.c

@@ -2617,7 +2617,9 @@ array_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     PyObject *initial = NULL, *it = NULL;
     const struct arraydescr *descr;
 
-    if (type == state->ArrayType && !_PyArg_NoKeywords("array.array", kwds))
+    if ((type == state->ArrayType ||
+         type->tp_init == state->ArrayType->tp_init) &&
+        !_PyArg_NoKeywords("array.array", kwds))
         return NULL;
 
     if (!PyArg_ParseTuple(args, "C|O:array", &c, &initial))