Make PyIter_Next() a little smarter (wrt its knowledge of iterator

internals) so clients can be a lot dumber (wrt their knowledge).

Include/abstract.h

@@ -484,9 +484,8 @@ xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx*/
      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. */
+	this returns NULL without setting an exception.
+	NULL with an exception means an error occurred. */
 
 /*  Number Protocol:*/
 

Objects/abstract.c

@@ -1276,18 +1276,10 @@ PySequence_List(PyObject *v)
 	for (i = 0; ; i++) {
 		PyObject *item = PyIter_Next(it);
 		if (item == NULL) {
-			/* We're out of here in any case, but if this is a
-			 * StopIteration exception it's expected, but if
-			 * any other kind of exception it's an error.
-			 */
 			if (PyErr_Occurred()) {
-				if (PyErr_ExceptionMatches(PyExc_StopIteration))
-					PyErr_Clear();
-				else {
 				Py_DECREF(result);
 				result = NULL;
 			}
-			}
 			break;
 		}
 		if (i < n)
@@ -1796,14 +1788,27 @@ PyObject_GetIter(PyObject *o)
 	}
 }
 
+/* Return next item.
+ * If an error occurs, return NULL.  PyErr_Occurred() will be true.
+ * If the iteration terminates normally, return NULL and clear the
+ * PyExc_StopIteration exception (if it was set).  PyErr_Occurred()
+ * will be false.
+ * Else return the next object.  PyErr_Occurred() will be false.
+ */
 PyObject *
 PyIter_Next(PyObject *iter)
 {
+	PyObject *result;
 	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);
+	result = (*iter->ob_type->tp_iternext)(iter);
+	if (result == NULL &&
+	    PyErr_Occurred() &&
+	    PyErr_ExceptionMatches(PyExc_StopIteration))
+		PyErr_Clear();
+	return result;
 }

Python/bltinmodule.c

@@ -164,7 +164,7 @@ builtin_filter(PyObject *self, PyObject *args)
 {
 	PyObject *func, *seq, *result, *it;
 	int len;   /* guess for result list size */
-	register int i, j;
+	register int j;
 
 	if (!PyArg_ParseTuple(args, "OO:filter", &func, &seq))
 		return NULL;
@@ -204,22 +204,15 @@ builtin_filter(PyObject *self, PyObject *args)
 	}
 
 	/* Build the result list. */
-	for (i = j = 0; ; ++i) {
+	j = 0;
+	for (;;) {
 		PyObject *item, *good;
 		int ok;
 
 		item = PyIter_Next(it);
 		if (item == NULL) {
-			/* We're out of here in any case, but if this is a
-			 * StopIteration exception it's expected, but if
-			 * any other kind of exception it's an error.
-			 */
-			if (PyErr_Occurred()) {
-				if (PyErr_ExceptionMatches(PyExc_StopIteration))
-					PyErr_Clear();
-				else
+			if (PyErr_Occurred())
 				goto Fail_result_it;
-			}
 			break;
 		}
 
@@ -1030,24 +1023,14 @@ builtin_map(PyObject *self, PyObject *args)
 				if (item)
 					++numactive;
 				else {
-					/* StopIteration is *implied* by a
-					 * NULL return from PyIter_Next() if
-					 * PyErr_Occurred() is false.
-					 */
 					if (PyErr_Occurred()) {
-						if (PyErr_ExceptionMatches(
-						    PyExc_StopIteration))
-							PyErr_Clear();
-						else {
 						Py_XDECREF(alist);
 						goto Fail_1;
 					}
-					}
 					Py_INCREF(Py_None);
 					item = Py_None;
 					sqp->saw_StopIteration = 1;
 				}
-
 			}
 			if (alist)
 				PyTuple_SET_ITEM(alist, j, item);
@@ -1445,7 +1428,6 @@ Return the dictionary containing the current scope's local variables.";
 static PyObject *
 min_max(PyObject *args, int op)
 {
-	int i;
 	PyObject *v, *w, *x, *it;
 
 	if (PyTuple_Size(args) > 1)
@@ -1458,22 +1440,14 @@ min_max(PyObject *args, int op)
 		return NULL;
 
 	w = NULL;  /* the result */
-	for (i = 0; ; i++) {
+	for (;;) {
 		x = PyIter_Next(it);
 		if (x == NULL) {
-			/* We're out of here in any case, but if this is a
-			 * StopIteration exception it's expected, but if
-			 * any other kind of exception it's an error.
-			 */
 			if (PyErr_Occurred()) {
-				if (PyErr_ExceptionMatches(PyExc_StopIteration))
-					PyErr_Clear();
-				else {
 				Py_XDECREF(w);
 				Py_DECREF(it);
 				return NULL;
 			}
-			}
 			break;
 		}
 
@@ -1880,15 +1854,8 @@ builtin_reduce(PyObject *self, PyObject *args)
 
 		op2 = PyIter_Next(it);
 		if (op2 == NULL) {
-			/* StopIteration is *implied* by a NULL return from
-			 * PyIter_Next() if PyErr_Occurred() is false.
-			 */
-			if (PyErr_Occurred()) {
-				if (PyErr_ExceptionMatches(PyExc_StopIteration))
-					PyErr_Clear();
-				else
+			if (PyErr_Occurred())
 				goto Fail;
-			}
  			break;
 		}
 

Python/ceval.c

@@ -1894,10 +1894,8 @@ eval_code2(PyCodeObject *co, PyObject *globals, PyObject *locals,
 				PUSH(x);
 				continue;
 			}
-			if (!PyErr_Occurred() ||
-			    PyErr_ExceptionMatches(
-				    PyExc_StopIteration))
-			{
+			if (!PyErr_Occurred()) {
+				/* iterator ended normally */
  				x = v = POP();
 				Py_DECREF(v);
 				JUMPBY(oparg);