* Beefed-up tests

* Allow tuple re-use
* Call tp_iternext directly

Lib/test/test_enumerate.py

 import unittest
+from sets import Set
 
 from test import test_support
 
-seq, res = 'abc', [(0,'a'), (1,'b'), (2,'c')]
-
 class G:
     'Sequence using __getitem__'
     def __init__(self, seqn):
@@ -65,37 +64,49 @@ class N:
 class EnumerateTestCase(unittest.TestCase):
 
     enum = enumerate
+    seq, res = 'abc', [(0,'a'), (1,'b'), (2,'c')]
 
     def test_basicfunction(self):
-        self.assertEqual(type(self.enum(seq)), self.enum)
-        e = self.enum(seq)
+        self.assertEqual(type(self.enum(self.seq)), self.enum)
+        e = self.enum(self.seq)
         self.assertEqual(iter(e), e)
-        self.assertEqual(list(self.enum(seq)), res)
+        self.assertEqual(list(self.enum(self.seq)), self.res)
         self.enum.__doc__
 
     def test_getitemseqn(self):
-        self.assertEqual(list(self.enum(G(seq))), res)
+        self.assertEqual(list(self.enum(G(self.seq))), self.res)
         e = self.enum(G(''))
         self.assertRaises(StopIteration, e.next)
 
     def test_iteratorseqn(self):
-        self.assertEqual(list(self.enum(I(seq))), res)
+        self.assertEqual(list(self.enum(I(self.seq))), self.res)
         e = self.enum(I(''))
         self.assertRaises(StopIteration, e.next)
 
     def test_iteratorgenerator(self):
-        self.assertEqual(list(self.enum(Ig(seq))), res)
+        self.assertEqual(list(self.enum(Ig(self.seq))), self.res)
         e = self.enum(Ig(''))
         self.assertRaises(StopIteration, e.next)
 
     def test_noniterable(self):
-        self.assertRaises(TypeError, self.enum, X(seq))
+        self.assertRaises(TypeError, self.enum, X(self.seq))
 
     def test_illformediterable(self):
-        self.assertRaises(TypeError, list, self.enum(N(seq)))
+        self.assertRaises(TypeError, list, self.enum(N(self.seq)))
 
     def test_exception_propagation(self):
-        self.assertRaises(ZeroDivisionError, list, self.enum(E(seq)))
+        self.assertRaises(ZeroDivisionError, list, self.enum(E(self.seq)))
+
+    def test_argumentcheck(self):
+        self.assertRaises(TypeError, self.enum) # no arguments
+        self.assertRaises(TypeError, self.enum, 1) # wrong type (not iterable)
+        self.assertRaises(TypeError, self.enum, 'abc', 2) # too many arguments
+
+    def test_tuple_reuse(self):
+        # Tests an implementation detail where tuple is reused
+        # whenever nothing else holds a reference to it
+        self.assertEqual(len(Set(map(id, list(self.seq)))), len(self.seq))
+        self.assertEqual(len(Set(map(id, enumerate(self.seq)))), min(1,len(self.seq)))
 
 class MyEnum(enumerate):
     pass
@@ -104,8 +115,28 @@ class SubclassTestCase(EnumerateTestCase):
 
     enum = MyEnum
 
-def test_main():
-    test_support.run_unittest(EnumerateTestCase, SubclassTestCase)
+class TestEmpty(EnumerateTestCase):
+
+    seq, res = '', []
+
+class TestBig(EnumerateTestCase):
+
+    seq = range(10,20000,2)
+    res = zip(range(20000), seq)
+
+
+def test_main(verbose=None):
+    testclasses = (EnumerateTestCase, SubclassTestCase, TestEmpty, TestBig)
+    test_support.run_unittest(*testclasses)
+
+    # verify reference counting
+    import sys
+    if verbose and hasattr(sys, "gettotalrefcount"):
+        counts = [None] * 5
+        for i in xrange(len(counts)):
+            test_support.run_unittest(*testclasses)
+            counts[i] = sys.gettotalrefcount()
+        print counts
 
 if __name__ == "__main__":
-    test_main()
+    test_main(verbose=True)

Objects/enumobject.c

@@ -6,6 +6,7 @@ typedef struct {
 	PyObject_HEAD
 	long      en_index;        /* current index of enumeration */
 	PyObject* en_sit;          /* secondary iterator of enumeration */
+	PyObject* en_result;	   /* result tuple  */
 } enumobject;
 
 PyTypeObject PyEnum_Type;
@@ -30,6 +31,16 @@ enum_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
 		Py_DECREF(en);
 		return NULL;
 	}
+	en->en_result = PyTuple_New(2);
+	if (en->en_result == NULL) {
+		Py_DECREF(en->en_sit);
+		Py_DECREF(en);
+		return NULL;
+	}
+	Py_INCREF(Py_None);
+	PyTuple_SET_ITEM(en->en_result, 0, Py_None);
+	Py_INCREF(Py_None);
+	PyTuple_SET_ITEM(en->en_result, 1, Py_None);
 	return (PyObject *)en;
 }
 
@@ -38,42 +49,60 @@ enum_dealloc(enumobject *en)
 {
 	PyObject_GC_UnTrack(en);
 	Py_XDECREF(en->en_sit);
+	Py_XDECREF(en->en_result);
 	en->ob_type->tp_free(en);
 }
 
 static int
 enum_traverse(enumobject *en, visitproc visit, void *arg)
 {
-	if (en->en_sit)
-		return visit(en->en_sit, arg);
+	int err;
+
+	if (en->en_sit) {
+		err = visit(en->en_sit, arg);
+		if (err)
+			return err;
+	}
+	if (en->en_result) {
+		err = visit(en->en_result, arg);
+		if (err)
+			return err;
+	}
 	return 0;
 }
 
 static PyObject *
 enum_next(enumobject *en)
 {
-	PyObject *result;
 	PyObject *next_index;
 	PyObject *next_item;
+	PyObject *result = en->en_result;
+	PyObject *it = en->en_sit;
 
-	result = PyTuple_New(2);
-	if (result == NULL)
+	next_item = (*it->ob_type->tp_iternext)(it);
+	if (next_item == NULL)
 		return NULL;
 
 	next_index = PyInt_FromLong(en->en_index);
 	if (next_index == NULL) {
-		Py_DECREF(result);
+		Py_DECREF(next_item);
 		return NULL;
 	}
-	PyTuple_SET_ITEM(result, 0, next_index);
+	en->en_index++;
 
-	next_item = PyIter_Next(en->en_sit);
-	if (next_item == NULL) {
-		Py_DECREF(result);
-		return NULL;
+	if (result->ob_refcnt == 1) {
+		Py_INCREF(result);
+		Py_DECREF(PyTuple_GET_ITEM(result, 0));
+		Py_DECREF(PyTuple_GET_ITEM(result, 1));
+	} else {
+		result = PyTuple_New(2);
+		if (result == NULL) {
+			Py_DECREF(next_index);
+			Py_DECREF(next_item);
+			return NULL;
+		}
 	}
-
-	en->en_index++;
+	PyTuple_SET_ITEM(result, 0, next_index);
 	PyTuple_SET_ITEM(result, 1, next_item);
 	return result;
 }