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bpo-44606: Fix __instancecheck__ and __subclasscheck__ for the union type. #27120

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Jul 14, 2021
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bpo-44606: Fix __instancecheck__ and __subclasscheck__ for the union type. #27120

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bpo-44606: Fix __instancecheck__ and __subclasscheck__ for the union …
serhiy-storchaka Jul 13, 2021
4167e19
Add test for virtual subclassing.
serhiy-storchaka Jul 13, 2021
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37 changes: 35 additions & 2 deletions Lib/test/test_types.py
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Original file line number Diff line number Diff line change
Expand Up @@ -661,6 +661,39 @@ def test_or_types_operator(self):
x.__args__ = [str, int]
(int | str ) == x

def test_instancecheck(self):
x = int | str
self.assertIsInstance(1, x)
self.assertIsInstance(True, x)
self.assertIsInstance('a', x)
self.assertNotIsInstance(None, x)
self.assertTrue(issubclass(int, x))
self.assertTrue(issubclass(bool, x))
self.assertTrue(issubclass(str, x))
self.assertFalse(issubclass(type(None), x))
x = int | None
self.assertIsInstance(None, x)
self.assertTrue(issubclass(type(None), x))
x = int | collections.abc.Mapping
self.assertIsInstance({}, x)
self.assertTrue(issubclass(dict, x))

def test_bad_instancecheck(self):
class BadMeta(type):
def __instancecheck__(cls, inst):
1/0
x = int | BadMeta('A', (), {})
self.assertTrue(isinstance(1, x))
self.assertRaises(ZeroDivisionError, isinstance, [], x)

def test_bad_subclasscheck(self):
class BadMeta(type):
def __subclasscheck__(cls, sub):
1/0
x = int | BadMeta('A', (), {})
self.assertTrue(issubclass(int, x))
self.assertRaises(ZeroDivisionError, issubclass, list, x)

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@Fidget-Spinner Fidget-Spinner Jul 13, 2021 •
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Maybe you can add your test from the bpo for virtual subclasses issubclass(dict, int | collections.abc.Mapping)?

Then again we may not need that test. If the previous tests throw the ZeroDivisionError, then that means it's already looking into the __subclasscheck__ dunder.

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Oh, I forget about this. Thank you for reminder.

def test_or_type_operator_with_TypeVar(self):
TV = typing.TypeVar('T')
assert TV | str == typing.Union[TV, str]
Expand Down Expand Up @@ -754,9 +787,9 @@ def __eq__(self, other):
for type_ in union_ga:
with self.subTest(f"check isinstance/issubclass is invalid for {type_}"):
with self.assertRaises(TypeError):
isinstance(list, type_)
isinstance(1, type_)
with self.assertRaises(TypeError):
issubclass(list, type_)
issubclass(int, type_)

def test_or_type_operator_with_bad_module(self):
class TypeVar:
Expand Down
1 change: 1 addition & 0 deletions Misc/NEWS.d/next/Core and Builtins/2021-07-13-20-22-12.bpo-44606.S3Bv2w.rst
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@@ -0,0 +1 @@
Fix ``__instancecheck__`` and ``__subclasscheck__`` for the union type.
23 changes: 19 additions & 4 deletions Objects/unionobject.c
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Original file line number Diff line number Diff line change
Expand Up @@ -70,8 +70,14 @@ union_instancecheck(PyObject *self, PyObject *instance)
if (arg == Py_None) {
arg = (PyObject *)&_PyNone_Type;
}
if (PyType_Check(arg) && PyObject_IsInstance(instance, arg) != 0) {
Py_RETURN_TRUE;
if (PyType_Check(arg)) {
int res = PyObject_IsInstance(instance, arg);
if (res < 0) {
return NULL;
}
if (res) {
Py_RETURN_TRUE;
}
}
}
Py_RETURN_FALSE;
Expand All @@ -93,8 +99,17 @@ union_subclasscheck(PyObject *self, PyObject *instance)
Py_ssize_t nargs = PyTuple_GET_SIZE(alias->args);
for (Py_ssize_t iarg = 0; iarg < nargs; iarg++) {
PyObject *arg = PyTuple_GET_ITEM(alias->args, iarg);
if (PyType_Check(arg) && (PyType_IsSubtype((PyTypeObject *)instance, (PyTypeObject *)arg) != 0)) {
Py_RETURN_TRUE;
if (arg == Py_None) {
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Reminder for myself that this can probably be removed when we do the auto conversion of None to type(None).

arg = (PyObject *)&_PyNone_Type;
}
if (PyType_Check(arg)) {
int res = PyObject_IsSubclass(instance, arg);
if (res < 0) {
return NULL;
}
if (res) {
Py_RETURN_TRUE;
}
}
}
Py_RETURN_FALSE;
Expand Down