Author: raymond.hettinger Date: Tue Nov 30 04:15:35 2010 New Revision: 86877 Log: Issue #10323: Predictable final state for slice(). Modified: python/branches/release27-maint/Lib/test/test_itertools.py python/branches/release27-maint/Misc/NEWS python/branches/release27-maint/Modules/itertoolsmodule.c Modified: python/branches/release27-maint/Lib/test/test_itertools.py ============================================================================== --- python/branches/release27-maint/Lib/test/test_itertools.py (original) +++ python/branches/release27-maint/Lib/test/test_itertools.py Tue Nov 30 04:15:35 2010 @@ -778,6 +778,11 @@ self.assertRaises(ValueError, islice, xrange(10), 1, 'a', 1) self.assertEqual(len(list(islice(count(), 1, 10, maxsize))), 1) + # Issue #10323: Less islice in a predictable state + c = count() + self.assertEqual(list(islice(c, 1, 3, 50)), [1]) + self.assertEqual(next(c), 3) + def test_takewhile(self): data = [1, 3, 5, 20, 2, 4, 6, 8] underten = lambda x: x<10 Modified: python/branches/release27-maint/Misc/NEWS ============================================================================== --- python/branches/release27-maint/Misc/NEWS (original) +++ python/branches/release27-maint/Misc/NEWS Tue Nov 30 04:15:35 2010 @@ -22,6 +22,10 @@ Library ------- +- Issue #10323: itertools.islice() now consumes the minimum number of + inputs before stopping. Formerly, the final state of the underlying + iterator was undefined. + - Issue #10565: The collections.Iterator ABC now checks for both ``__iter__`` and ``next``. Modified: python/branches/release27-maint/Modules/itertoolsmodule.c ============================================================================== --- python/branches/release27-maint/Modules/itertoolsmodule.c (original) +++ python/branches/release27-maint/Modules/itertoolsmodule.c Tue Nov 30 04:15:35 2010 @@ -1215,6 +1215,7 @@ { PyObject *item; PyObject *it = lz->it; + Py_ssize_t stop = lz->stop; Py_ssize_t oldnext; PyObject *(*iternext)(PyObject *); @@ -1226,7 +1227,7 @@ Py_DECREF(item); lz->cnt++; } - if (lz->stop != -1 && lz->cnt >= lz->stop) + if (stop != -1 && lz->cnt >= stop) return NULL; item = iternext(it); if (item == NULL) @@ -1234,8 +1235,8 @@ lz->cnt++; oldnext = lz->next; lz->next += lz->step; - if (lz->next < oldnext) /* Check for overflow */ - lz->next = lz->stop; + if (lz->next < oldnext || (stop != -1 && lz->next > stop)) + lz->next = stop; return item; }