Keir Mierle's set operations for dict views (keys/items only of course).

Lib/test/test_dict.py

@@ -458,6 +458,23 @@ class DictTest(unittest.TestCase):
         self.assertRaises(RuntimeError, lambda: d2.items() < d3.items())
         self.assertRaises(RuntimeError, lambda: d3.items() > d2.items())
 
+    def test_dictview_set_operations(self):
+        k1 = {1:1, 2:2}.keys()
+        k2 = {1:1, 2:2, 3:3}.keys()
+        k3 = {4:4}.keys()
+
+        self.assertEquals(k1 - k2, set())
+        self.assertEquals(k1 - k3, {1,2})
+        self.assertEquals(k2 - k1, {3})
+        self.assertEquals(k3 - k1, {4})
+        self.assertEquals(k1 & k2, {1,2})
+        self.assertEquals(k1 & k3, set())
+        self.assertEquals(k1 | k2, {1,2,3})
+        self.assertEquals(k1 ^ k2, {3})
+        self.assertEquals(k1 ^ k3, {1,2,4})
+
+        # XXX similar tests for .items()
+
     def test_missing(self):
         # Make sure dict doesn't have a __missing__ method
         self.assertEqual(hasattr(dict, "__missing__"), False)

Objects/dictobject.c

@@ -2489,6 +2489,98 @@ static PySequenceMethods dictkeys_as_sequence = {
 	(objobjproc)dictkeys_contains,	/* sq_contains */
 };
 
+static PyObject*
+dictviews_sub(PyObject* self, PyObject *other)
+{
+	PyObject *result = PySet_New(self);
+	PyObject *tmp;
+	if (result == NULL)
+		return NULL;
+
+	tmp = PyObject_CallMethod(result, "difference_update", "O", other);
+	if (tmp == NULL) {
+		Py_DECREF(result);
+		return NULL;
+	}
+
+	Py_DECREF(tmp);
+	return result;
+}
+
+static PyObject*
+dictviews_and(PyObject* self, PyObject *other)
+{
+	PyObject *result = PySet_New(self);
+	PyObject *tmp;
+	if (result == NULL)
+		return NULL;
+
+	tmp = PyObject_CallMethod(result, "intersection_update", "O", other);
+	if (tmp == NULL) {
+		Py_DECREF(result);
+		return NULL;
+	}
+
+	Py_DECREF(tmp);
+	return result;
+}
+
+static PyObject*
+dictviews_or(PyObject* self, PyObject *other)
+{
+	PyObject *result = PySet_New(self);
+	PyObject *tmp;
+	if (result == NULL)
+		return NULL;
+
+	tmp = PyObject_CallMethod(result, "update", "O", other);
+	if (tmp == NULL) {
+		Py_DECREF(result);
+		return NULL;
+	}
+
+	Py_DECREF(tmp);
+	return result;
+}
+
+static PyObject*
+dictviews_xor(PyObject* self, PyObject *other)
+{
+	PyObject *result = PySet_New(self);
+	PyObject *tmp;
+	if (result == NULL)
+		return NULL;
+
+	tmp = PyObject_CallMethod(result, "symmetric_difference_update", "O",
+				  other);
+	if (tmp == NULL) {
+		Py_DECREF(result);
+		return NULL;
+	}
+
+	Py_DECREF(tmp);
+	return result;
+}
+
+static PyNumberMethods dictviews_as_number = {
+	0,				/*nb_add*/
+	(binaryfunc)dictviews_sub,	/*nb_subtract*/
+	0,				/*nb_multiply*/
+	0,				/*nb_remainder*/
+	0,				/*nb_divmod*/
+	0,				/*nb_power*/
+	0,				/*nb_negative*/
+	0,				/*nb_positive*/
+	0,				/*nb_absolute*/
+	0,				/*nb_bool*/
+	0,				/*nb_invert*/
+	0,				/*nb_lshift*/
+	0,				/*nb_rshift*/
+	(binaryfunc)dictviews_and,	/*nb_and*/
+	(binaryfunc)dictviews_xor,	/*nb_xor*/
+	(binaryfunc)dictviews_or,	/*nb_or*/
+};
+
 static PyMethodDef dictkeys_methods[] = {
  	{NULL,		NULL}		/* sentinel */
 };
@@ -2505,7 +2597,7 @@ PyTypeObject PyDictKeys_Type = {
 	0,					/* tp_setattr */
 	0,					/* tp_compare */
 	0,					/* tp_repr */
-	0,					/* tp_as_number */
+	&dictviews_as_number,			/* tp_as_number */
 	&dictkeys_as_sequence,			/* tp_as_sequence */
 	0,					/* tp_as_mapping */
 	0,					/* tp_hash */
@@ -2589,7 +2681,7 @@ PyTypeObject PyDictItems_Type = {
 	0,					/* tp_setattr */
 	0,					/* tp_compare */
 	0,					/* tp_repr */
-	0,					/* tp_as_number */
+	&dictviews_as_number,			/* tp_as_number */
 	&dictitems_as_sequence,			/* tp_as_sequence */
 	0,					/* tp_as_mapping */
 	0,					/* tp_hash */