Let set.union() and set.update() accept multiple inputs.

Doc/library/stdtypes.rst

@@ -1567,11 +1567,14 @@ The constructors for both classes work the same:
       Test whether the set is a true superset of *other*, that is, ``set >=
       other and set != other``.
 
-   .. method:: union(other)
+   .. method:: union(other, ...)
-               set | other
+               set | other | ...
 
       Return a new set with elements from both sets.
 
+      .. versionchanged:: 2.6
+         Accepts multiple input iterables.
+
    .. method:: intersection(other)
                set & other
 
@@ -1628,11 +1631,14 @@ The constructors for both classes work the same:
    The following table lists operations available for :class:`set` that do not
    apply to immutable instances of :class:`frozenset`:
 
-   .. method:: update(other)
+   .. method:: update(other, ...)
-               set |= other
+               set |= other | ...
 
       Update the set, adding elements from *other*.
 
+      .. versionchanged:: 2.6
+         Accepts multiple input iterables.
+
    .. method:: intersection_update(other)
                set &= other
 

Lib/test/test_set.py

@@ -78,6 +78,7 @@ class TestJointOps(unittest.TestCase):
             self.assertEqual(self.thetype('abcba').union(C('efgfe')), set('abcefg'))
             self.assertEqual(self.thetype('abcba').union(C('ccb')), set('abc'))
             self.assertEqual(self.thetype('abcba').union(C('ef')), set('abcef'))
+            self.assertEqual(self.thetype('abcba').union(C('ef'), C('fg')), set('abcefg'))
 
     def test_or(self):
         i = self.s.union(self.otherword)
@@ -401,6 +402,12 @@ class TestSet(TestJointOps):
                 s = self.thetype('abcba')
                 self.assertEqual(s.update(C(p)), None)
                 self.assertEqual(s, set(q))
+        for p in ('cdc', 'efgfe', 'ccb', 'ef', 'abcda'):
+            q = 'ahi'
+            for C in set, frozenset, dict.fromkeys, str, unicode, list, tuple:
+                s = self.thetype('abcba')
+                self.assertEqual(s.update(C(p), C(q)), None)
+                self.assertEqual(s, set(s) | set(p) | set(q))
 
     def test_ior(self):
         self.s |= set(self.otherword)

Misc/NEWS

@@ -12,6 +12,8 @@ What's New in Python 2.6 beta 1?
 Core and Builtins
 -----------------
 
+- The set methods, update() and union() now accept multiple arguments.
+
 - Issue #2898: Added sys.getsizeof() to retrieve size of objects in bytes.
 
 - New environment variable PYTHONIOENCODING.

Objects/setobject.c

@@ -967,15 +967,20 @@ set_update_internal(PySetObject *so, PyObject *other)
 }
 
 static PyObject *
-set_update(PySetObject *so, PyObject *other)
+set_update(PySetObject *so, PyObject *args)
 {
+	Py_ssize_t i;
+
+	for (i=0 ; i<PyTuple_GET_SIZE(args) ; i++) {
+		PyObject *other = PyTuple_GET_ITEM(args, i);
 		if (set_update_internal(so, other) == -1)
 			return NULL;
+	}
 	Py_RETURN_NONE;
 }
 
 PyDoc_STRVAR(update_doc, 
-"Update a set with the union of itself and another.");
+"Update a set with the union of itself and others.");
 
 static PyObject *
 make_new_set(PyTypeObject *type, PyObject *iterable)
@@ -1156,9 +1161,42 @@ set_clear(PySetObject *so)
 PyDoc_STRVAR(clear_doc, "Remove all elements from this set.");
 
 static PyObject *
-set_union(PySetObject *so, PyObject *other)
+set_union(PySetObject *so, PyObject *args)
 {
 	PySetObject *result;
+	PyObject *other;
+	Py_ssize_t i;
+
+	result = (PySetObject *)set_copy(so);
+	if (result == NULL)
+		return NULL;
+
+	for (i=0 ; i<PyTuple_GET_SIZE(args) ; i++) {
+		other = PyTuple_GET_ITEM(args, i);
+		if ((PyObject *)so == other)
+			return (PyObject *)result;
+		if (set_update_internal(result, other) == -1) {
+			Py_DECREF(result);
+			return NULL;
+		}
+	}
+	return (PyObject *)result;
+}
+
+PyDoc_STRVAR(union_doc,
+ "Return the union of sets as a new set.\n\
+\n\
+(i.e. all elements that are in either set.)");
+
+static PyObject *
+set_or(PySetObject *so, PyObject *other)
+{
+	PySetObject *result;
+
+	if (!PyAnySet_Check(so) || !PyAnySet_Check(other)) {
+		Py_INCREF(Py_NotImplemented);
+		return Py_NotImplemented;
+	}
 
 	result = (PySetObject *)set_copy(so);
 	if (result == NULL)
@@ -1172,21 +1210,6 @@ set_union(PySetObject *so, PyObject *other)
 	return (PyObject *)result;
 }
 
-PyDoc_STRVAR(union_doc,
- "Return the union of two sets as a new set.\n\
-\n\
-(i.e. all elements that are in either set.)");
-
-static PyObject *
-set_or(PySetObject *so, PyObject *other)
-{
-	if (!PyAnySet_Check(so) || !PyAnySet_Check(other)) {
-		Py_INCREF(Py_NotImplemented);
-		return Py_NotImplemented;
-	}
-	return set_union(so, other);
-}
-
 static PyObject *
 set_ior(PySetObject *so, PyObject *other)
 {
@@ -1947,9 +1970,9 @@ static PyMethodDef set_methods[] = {
 	{"test_c_api",	(PyCFunction)test_c_api,	METH_NOARGS,
 	 test_c_api_doc},
 #endif
-	{"union",	(PyCFunction)set_union,		METH_O,
+	{"union",	(PyCFunction)set_union,		METH_VARARGS,
 	 union_doc},
-	{"update",	(PyCFunction)set_update,	METH_O,
+	{"update",	(PyCFunction)set_update,	METH_VARARGS,
 	 update_doc},
 	{NULL,		NULL}	/* sentinel */
 };
@@ -2062,7 +2085,7 @@ static PyMethodDef frozenset_methods[] = {
 	 reduce_doc},
 	{"symmetric_difference",(PyCFunction)set_symmetric_difference,	METH_O,
 	 symmetric_difference_doc},
-	{"union",	(PyCFunction)set_union,		METH_O,
+	{"union",	(PyCFunction)set_union,		METH_VARARGS,
 	 union_doc},
 	{NULL,		NULL}	/* sentinel */
 };