[Python-checkins] r86876 - in python/branches/release31-maint: Lib/test/test_itertools.py Misc/NEWS Modules/itertoolsmodule.c

Tue Nov 30 04:09:05 CET 2010

Author: raymond.hettinger
Date: Tue Nov 30 04:09:05 2010
New Revision: 86876
Log:
Issue #10323: Predictable final state for slice().
Modified:
 python/branches/release31-maint/Lib/test/test_itertools.py
 python/branches/release31-maint/Misc/NEWS
 python/branches/release31-maint/Modules/itertoolsmodule.c
Modified: python/branches/release31-maint/Lib/test/test_itertools.py
==============================================================================

--- python/branches/release31-maint/Lib/test/test_itertools.py	(original)
+++ python/branches/release31-maint/Lib/test/test_itertools.py	Tue Nov 30 04:09:05 2010
@@ -788,6 +788,11 @@
 self.assertRaises(ValueError, islice, range(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/release31-maint/Misc/NEWS
==============================================================================
--- python/branches/release31-maint/Misc/NEWS	(original)
+++ python/branches/release31-maint/Misc/NEWS	Tue Nov 30 04:09:05 2010
@@ -28,6 +28,10 @@
 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/release31-maint/Modules/itertoolsmodule.c
==============================================================================
--- python/branches/release31-maint/Modules/itertoolsmodule.c	(original)
+++ python/branches/release31-maint/Modules/itertoolsmodule.c	Tue Nov 30 04:09:05 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;
 }
 
