Make isinstance and issubclass error for GenericAlias (python#6)

Lib/test/test_genericalias.py

@@ -161,6 +161,17 @@ def test_equality(self):
         self.assertNotEqual(list, list[int])
         self.assertNotEqual(list[int], list)
 
+    def test_isinstance(self):
+        self.assertTrue(isinstance([], list))
+        with self.assertRaises(TypeError):
+            isinstance([], list[str])
+
+    def test_issubclass(self):
+        class L(list): ...
+        self.assertTrue(issubclass(L, list))
+        with self.assertRaises(TypeError):
+            issubclass(L, list[str])
+
 
 if __name__ == "__main__":
     unittest.main()

Objects/descrobject.c

@@ -2061,8 +2061,26 @@ ga_mro_entries(PyObject *self, PyObject *args)
     return PyTuple_Pack(1, alias->origin);
 }
 
+static PyObject *
+ga_instancecheck(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    return PyErr_Format(PyExc_TypeError,
+                        "TypeError: Subscripted generics cannot be used with class and instance checks",
+                        self);
+}
+
+static PyObject *
+ga_subclasscheck(PyObject *self, PyObject *Py_UNUSED(ignored))
+{
+    return PyErr_Format(PyExc_TypeError,
+                        "TypeError: Subscripted generics cannot be used with class and instance checks",
+                        self);
+}
+
 static PyMethodDef ga_methods[] = {
     {"__mro_entries__", ga_mro_entries, METH_O},
+    {"__instancecheck__", ga_instancecheck, METH_O},
+    {"__subclasscheck__", ga_subclasscheck, METH_O},
     {0}
 };