Bugfix: Properly test for errors from PyLong_AsLong() in itertools.cycle.

ti can raise an exception even if PyLong_Check() has
succeeded.

Lib/test/test_itertools.py

@@ -339,6 +339,8 @@ class TestBasicOps(unittest.TestCase):
                          list(range(maxsize-5, maxsize+5)))
         self.assertEqual(list(islice(count(-maxsize-5), 10)),
                          list(range(-maxsize-5, -maxsize+5)))
+        self.assertEqual(list(islice(count(10, maxsize+5), 3)),
+                         list(range(10, 10+3*(maxsize+5), maxsize+5)))
         c = count(3)
         self.assertEqual(repr(c), 'count(3)')
         next(c)
@@ -361,6 +363,9 @@ class TestBasicOps(unittest.TestCase):
             self.assertEqual(next(copy.deepcopy(c)), value)
             self.assertEqual(next(pickle.loads(pickle.dumps(c))), value)
 
+        #check proper internal error handling for large "step' sizes
+        count(1, maxsize+5); sys.exc_info()
+
     def test_count_with_stride(self):
         self.assertEqual(lzip('abc',count(2,3)), [('a', 2), ('b', 5), ('c', 8)])
         self.assertEqual(lzip('abc',count(start=2,step=3)),

Modules/itertoolsmodule.c

@@ -2918,6 +2918,7 @@ count_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     Py_ssize_t cnt = 0;
     PyObject *long_cnt = NULL;
     PyObject *long_step = NULL;
+    long step;
     static char *kwlist[] = {"start", "step", 0};
 
     if (!PyArg_ParseTupleAndKeywords(args, kwds, "|OO:count",
@@ -2955,9 +2956,11 @@ count_new(PyTypeObject *type, PyObject *args, PyObject *kwds)
     assert(long_cnt != NULL && long_step != NULL);
 
     /* Fast mode only works when the step is 1 */
-    if (!PyLong_Check(long_step) ||
-        PyLong_AS_LONG(long_step) != 1) {
+    step = PyLong_AsLong(long_step);
+    if (step != 1) {
         slow_mode = 1;
+        if (step == -1 && PyErr_Occurred())
+            PyErr_Clear();
     }
 
     if (slow_mode)