Mondo changes to the iterator stuff, without changing how Python code

sees it (test_iter.py is unchanged).

- Added a tp_iternext slot, which calls the iterator's next() method;
  this is much faster for built-in iterators over built-in types
  such as lists and dicts, speeding up pybench's ForLoop with about
  25% compared to Python 2.1.  (Now there's a good argument for
  iterators. ;-)

- Renamed the built-in sequence iterator SeqIter, affecting the C API
  functions for it.  (This frees up the PyIter prefix for generic
  iterator operations.)

- Added PyIter_Check(obj), which checks that obj's type has a
  tp_iternext slot and that the proper feature flag is set.

- Added PyIter_Next(obj) which calls the tp_iternext slot.  It has a
  somewhat complex return condition due to the need for speed: when it
  returns NULL, it may not have set an exception condition, meaning
  the iterator is exhausted; when the exception StopIteration is set
  (or a derived exception class), it means the same thing; any other
  exception means some other error occurred.

Include/abstract.h

@@ -470,11 +470,24 @@ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*/
 
        */
 
+/* Iterators */
+
      DL_IMPORT(PyObject *) PyObject_GetIter(PyObject *);
      /* Takes an object and returns an iterator for it.
         This is typically a new iterator but if the argument
 	is an iterator, this returns itself. */
 
+#define PyIter_Check(obj) \
+    (PyType_HasFeature((obj)->ob_type, Py_TPFLAGS_HAVE_ITER) && \
+     (obj)->ob_type->tp_iternext != NULL)
+
+     DL_IMPORT(PyObject *) PyIter_Next(PyObject *);
+     /* Takes an iterator object and calls its tp_iternext slot,
+	returning the next value.  If the iterator is exhausted,
+	this can return NULL without setting an exception, *or*
+	NULL with a StopIteration exception.
+	NULL with any other exception  means an error occurred. */
+
 /*  Number Protocol:*/
 
      DL_IMPORT(int) PyNumber_Check(PyObject *o);

Include/iterobject.h

@@ -1,10 +1,10 @@
 /* Iterators (the basic kind, over a sequence) */
 
-extern DL_IMPORT(PyTypeObject) PyIter_Type;
+extern DL_IMPORT(PyTypeObject) PySeqIter_Type;
 
-#define PyIter_Check(op) ((op)->ob_type == &PyIter_Type)
+#define PySeqIter_Check(op) ((op)->ob_type == &PySeqIter_Type)
 
-extern DL_IMPORT(PyObject *) PyIter_New(PyObject *);
+extern DL_IMPORT(PyObject *) PySeqIter_New(PyObject *);
 
 extern DL_IMPORT(PyTypeObject) PyCallIter_Type;
 

Include/object.h

@@ -201,6 +201,7 @@ typedef PyObject *(*reprfunc)(PyObject *);
 typedef long (*hashfunc)(PyObject *);
 typedef PyObject *(*richcmpfunc) (PyObject *, PyObject *, int);
 typedef PyObject *(*getiterfunc) (PyObject *);
+typedef PyObject *(*iternextfunc) (PyObject *);
 
 typedef struct _typeobject {
 	PyObject_VAR_HEAD
@@ -252,6 +253,7 @@ typedef struct _typeobject {
 
 	/* Iterators */
 	getiterfunc tp_iter;
+	iternextfunc tp_iternext;
 
 #ifdef COUNT_ALLOCS
 	/* these must be last and never explicitly initialized */

Objects/abstract.c

@@ -1748,10 +1748,32 @@ PyObject_GetIter(PyObject *o)
 		f = t->tp_iter;
 	if (f == NULL) {
 		if (PySequence_Check(o))
-			return PyIter_New(o);
+			return PySeqIter_New(o);
 		PyErr_SetString(PyExc_TypeError, "iter() of non-sequence");
 		return NULL;
 	}
-	else
-		return (*f)(o);
+	else {
+		PyObject *res = (*f)(o);
+		if (res != NULL && !PyIter_Check(res)) {
+			PyErr_Format(PyExc_TypeError,
+				     "iter() returned non-iterator "
+				     "of type '%.100s'",
+				     res->ob_type->tp_name);
+			Py_DECREF(res);
+			res = NULL;
+		}
+		return res;
+	}
+}
+
+PyObject *
+PyIter_Next(PyObject *iter)
+{
+	if (!PyIter_Check(iter)) {
+		PyErr_Format(PyExc_TypeError,
+			     "'%.100s' object is not an iterator",
+			     iter->ob_type->tp_name);
+		return NULL;
+	}
+	return (*iter->ob_type->tp_iternext)(iter);
 }

Objects/classobject.c

@@ -848,7 +848,8 @@ instance_traverse(PyInstanceObject *o, visitproc visit, void *arg)
 	return 0;
 }
 
-static PyObject *getitemstr, *setitemstr, *delitemstr, *lenstr, *iterstr;
+static PyObject *getitemstr, *setitemstr, *delitemstr, *lenstr;
+static PyObject *iterstr, *nextstr;
 
 static int
 instance_length(PyInstanceObject *inst)
@@ -1726,6 +1727,14 @@ instance_getiter(PyInstanceObject *self)
 	if ((func = instance_getattr(self, iterstr)) != NULL) {
 		PyObject *res = PyEval_CallObject(func, (PyObject *)NULL);
 		Py_DECREF(func);
+		if (res != NULL && !PyIter_Check(res)) {
+			PyErr_Format(PyExc_TypeError,
+				     "__iter__ returned non-iterator "
+				     "of type '%.100s'",
+				     res->ob_type->tp_name);
+			Py_DECREF(res);
+			res = NULL;
+		}
 		return res;
 	}
 	PyErr_Clear();
@@ -1734,7 +1743,33 @@ instance_getiter(PyInstanceObject *self)
 		return NULL;
 	}
 	Py_DECREF(func);
-	return PyIter_New((PyObject *)self);
+	return PySeqIter_New((PyObject *)self);
+}
+
+
+/* Call the iterator's next */
+static PyObject *
+instance_iternext(PyInstanceObject *self)
+{
+	PyObject *func;
+
+	if (nextstr == NULL)
+		nextstr = PyString_InternFromString("next");
+
+	if ((func = instance_getattr(self, nextstr)) != NULL) {
+		PyObject *res = PyEval_CallObject(func, (PyObject *)NULL);
+		Py_DECREF(func);
+		if (res != NULL) {
+			return res;
+		}
+		if (PyErr_ExceptionMatches(PyExc_StopIteration)) {
+			PyErr_Clear();
+			return NULL;
+		}
+		return NULL;
+	}
+	PyErr_SetString(PyExc_TypeError, "instance has no next() method");
+	return NULL;
 }
 
 
@@ -1803,6 +1838,7 @@ PyTypeObject PyInstance_Type = {
 	instance_richcompare,			/* tp_richcompare */
  	offsetof(PyInstanceObject, in_weakreflist), /* tp_weaklistoffset */
 	(getiterfunc)instance_getiter,		/* tp_iter */
+	(iternextfunc)instance_iternext,	/* tp_iternext */
 };
 
 

Objects/dictobject.c

@@ -1354,6 +1354,7 @@ PyTypeObject PyDict_Type = {
 	0,					/* tp_richcompare */
 	0,					/* tp_weaklistoffset */
 	(getiterfunc)dictiter_new,		/* tp_iter */
+	0,					/* tp_iternext */
 };
 
 /* For backward compatibility with old dictionary interface */
@@ -1433,6 +1434,7 @@ static PyObject *
 dictiter_next(dictiterobject *di, PyObject *args)
 {
 	PyObject *key;
+
 	if (di->di_size != di->di_dict->ma_size) {
 		PyErr_SetString(PyExc_RuntimeError,
 				"dictionary changed size during iteration");
@@ -1460,9 +1462,25 @@ static PyMethodDef dictiter_methods[] = {
 };
 
 static PyObject *
-dictiter_getattr(dictiterobject *it, char *name)
+dictiter_getattr(dictiterobject *di, char *name)
 {
-	return Py_FindMethod(dictiter_methods, (PyObject *)it, name);
+	return Py_FindMethod(dictiter_methods, (PyObject *)di, name);
+}
+
+static PyObject *dictiter_iternext(dictiterobject *di)
+{
+	PyObject *key;
+
+	if (di->di_size != di->di_dict->ma_size) {
+		PyErr_SetString(PyExc_RuntimeError,
+				"dictionary changed size during iteration");
+		return NULL;
+	}
+	if (PyDict_Next((PyObject *)(di->di_dict), &di->di_pos, &key, NULL)) {
+		Py_INCREF(key);
+		return key;
+	}
+	return NULL;
 }
 
 PyTypeObject PyDictIter_Type = {
@@ -1494,4 +1512,5 @@ PyTypeObject PyDictIter_Type = {
 	0,					/* tp_richcompare */
 	0,					/* tp_weaklistoffset */
 	(getiterfunc)dictiter_getiter,		/* tp_iter */
+	(iternextfunc)dictiter_iternext,	/* tp_iternext */
 };

Objects/fileobject.c

@@ -1340,6 +1340,7 @@ PyTypeObject PyFile_Type = {
 	0,					/* tp_richcompare */
 	0,					/* tp_weaklistoffset */
 	(getiterfunc)file_getiter,		/* tp_iter */
+	0,					/* tp_iternext */
 };
 
 /* Interface for the 'soft space' between print items. */

Objects/iterobject.c

@@ -6,13 +6,13 @@ typedef struct {
 	PyObject_HEAD
 	long      it_index;
 	PyObject *it_seq;
-} iterobject;
+} seqiterobject;
 
 PyObject *
-PyIter_New(PyObject *seq)
+PySeqIter_New(PyObject *seq)
 {
-	iterobject *it;
-	it = PyObject_NEW(iterobject, &PyIter_Type);
+	seqiterobject *it;
+	it = PyObject_NEW(seqiterobject, &PySeqIter_Type);
 	if (it == NULL)
 		return NULL;
 	it->it_index = 0;
@@ -21,36 +21,22 @@ PyIter_New(PyObject *seq)
 	return (PyObject *)it;
 }
 static void
-iter_dealloc(iterobject *it)
+iter_dealloc(seqiterobject *it)
 {
 	Py_DECREF(it->it_seq);
 	PyObject_DEL(it);
 }
 
 static PyObject *
-iter_next(iterobject *it, PyObject *args)
+iter_next(seqiterobject *it, PyObject *args)
 {
 	PyObject *seq = it->it_seq;
-
-	if (PyList_Check(seq)) {
-		PyObject *item;
-		if (it->it_index >= PyList_GET_SIZE(seq)) {
-			PyErr_SetObject(PyExc_StopIteration, Py_None);
-			return NULL;
-		}
-		item = PyList_GET_ITEM(seq, it->it_index);
-		it->it_index++;
-		Py_INCREF(item);
-		return item;
-	}
-	else {
 	PyObject *result = PySequence_GetItem(seq, it->it_index++);
-		if (result == NULL &&
-		    PyErr_ExceptionMatches(PyExc_IndexError))
+
+	if (result == NULL && PyErr_ExceptionMatches(PyExc_IndexError))
 		PyErr_SetObject(PyExc_StopIteration, Py_None);
 	return result;
 }
-}
 
 static PyObject *
 iter_getiter(PyObject *it)
@@ -59,6 +45,43 @@ iter_getiter(PyObject *it)
 	return it;
 }
 
+/* Return (value, 0) if OK; (NULL, 0) at end; (NULL, -1) if exception */
+static PyObject *
+iter_iternext(PyObject *iterator)
+{
+	seqiterobject *it;
+	PyObject *seq;
+
+	assert(PySeqIter_Check(iterator));
+	it = (seqiterobject *)iterator;
+	seq = it->it_seq;
+
+	if (PyList_Check(seq)) {
+		PyObject *item;
+		if (it->it_index >= PyList_GET_SIZE(seq)) {
+			return NULL;
+		}
+		item = PyList_GET_ITEM(seq, it->it_index);
+		it->it_index++;
+		Py_INCREF(item);
+		return item;
+	}
+	else {
+		PyObject *result = PySequence_GetItem(seq, it->it_index++);
+		if (result != NULL) {
+			return result;
+		}
+		if (PyErr_ExceptionMatches(PyExc_IndexError) ||
+			PyErr_ExceptionMatches(PyExc_StopIteration)) {
+			PyErr_Clear();
+			return NULL;
+		}
+		else {
+			return NULL;
+		}
+	}
+}
+
 static PyMethodDef iter_methods[] = {
 	{"next",	(PyCFunction)iter_next,	METH_VARARGS,
 	 "it.next() -- get the next value, or raise StopIteration"},
@@ -66,16 +89,16 @@ static PyMethodDef iter_methods[] = {
 };
 
 static PyObject *
-iter_getattr(iterobject *it, char *name)
+iter_getattr(seqiterobject *it, char *name)
 {
 	return Py_FindMethod(iter_methods, (PyObject *)it, name);
 }
 
-PyTypeObject PyIter_Type = {
+PyTypeObject PySeqIter_Type = {
 	PyObject_HEAD_INIT(&PyType_Type)
 	0,					/* ob_size */
 	"iterator",				/* tp_name */
-	sizeof(iterobject),			/* tp_basicsize */
+	sizeof(seqiterobject),			/* tp_basicsize */
 	0,					/* tp_itemsize */
 	/* methods */
 	(destructor)iter_dealloc, 		/* tp_dealloc */
@@ -100,6 +123,7 @@ PyTypeObject PyIter_Type = {
 	0,					/* tp_richcompare */
 	0,					/* tp_weaklistoffset */
 	(getiterfunc)iter_getiter,		/* tp_iter */
+	(iternextfunc)iter_iternext,		/* tp_iternext */
 };
 
 /* -------------------------------------- */
@@ -130,6 +154,7 @@ calliter_dealloc(calliterobject *it)
 	Py_DECREF(it->it_sentinel);
 	PyObject_DEL(it);
 }
+
 static PyObject *
 calliter_next(calliterobject *it, PyObject *args)
 {
@@ -156,6 +181,22 @@ calliter_getattr(calliterobject *it, char *name)
 	return Py_FindMethod(calliter_methods, (PyObject *)it, name);
 }
 
+static PyObject *
+calliter_iternext(calliterobject *it)
+{
+	PyObject *result = PyObject_CallObject(it->it_callable, NULL);
+	if (result != NULL) {
+		if (PyObject_RichCompareBool(result, it->it_sentinel, Py_EQ)) {
+			Py_DECREF(result);
+			result = NULL;
+		}
+	}
+	else if (PyErr_ExceptionMatches(PyExc_StopIteration)) {
+		PyErr_Clear();
+	}
+	return result;
+}
+
 PyTypeObject PyCallIter_Type = {
 	PyObject_HEAD_INIT(&PyType_Type)
 	0,					/* ob_size */
@@ -185,4 +226,5 @@ PyTypeObject PyCallIter_Type = {
 	0,					/* tp_richcompare */
 	0,					/* tp_weaklistoffset */
 	(getiterfunc)iter_getiter,		/* tp_iter */
+	(iternextfunc)calliter_iternext,	/* tp_iternext */
 };

Python/ceval.c

@@ -381,7 +381,6 @@ eval_code2(PyCodeObject *co, PyObject *globals, PyObject *locals,
 	/* Make it easier to find out where we are with a debugger */
 	char *filename = PyString_AsString(co->co_filename);
 #endif
-	static PyObject *nextstr;
 
 /* Code access macros */
 
@@ -417,11 +416,6 @@ eval_code2(PyCodeObject *co, PyObject *globals, PyObject *locals,
 				     GETLOCAL(i) = value; } while (0)
 
 /* Start of code */
-	if (nextstr == NULL) {
-		nextstr = PyString_InternFromString("next");
-		if (nextstr == NULL)
-			return NULL;
-	}
 
 #ifdef USE_STACKCHECK
 	if (tstate->recursion_depth%10 == 0 && PyOS_CheckStack()) {
@@ -1886,35 +1880,30 @@ eval_code2(PyCodeObject *co, PyObject *globals, PyObject *locals,
 			v = POP();
 			x = PyObject_GetIter(v);
 			Py_DECREF(v);
-			if (x != NULL) {
-				w = x;
-				x = PyObject_GetAttr(w, nextstr);
-				Py_DECREF(w);
 			if (x != NULL) {
 				PUSH(x);
 				continue;
 			}
-			}
 			break;
 
 		case FOR_ITER:
 			/* before: [iter]; after: [iter, iter()] *or* [] */
 			v = TOP();
-			x = PyObject_CallObject(v, NULL);
-			if (x == NULL) {
-				if (PyErr_ExceptionMatches(
+			x = PyIter_Next(v);
+			if (x != NULL) {
+				PUSH(x);
+				continue;
+			}
+			if (!PyErr_Occurred() ||
+			    PyErr_ExceptionMatches(
 				    PyExc_StopIteration))
 			{
-					PyErr_Clear();
 				x = v = POP();
 				Py_DECREF(v);
 				JUMPBY(oparg);
 				continue;
 			}
 			break;
-			}
-			PUSH(x);
-			continue;
 
 		case FOR_LOOP:
 			/* for v in s: ...