Issue #3004: Minor fix to slice.indices(). slice(-10).indices(9) now

returns (0, 0, 1) instead of (0, -1, 1), and slice(None, 10, -1).indices(10)
returns (9, 9, -1) instead of (9, 10, -1).

Lib/test/test_slice.py

@@ -79,6 +79,20 @@ class SliceTest(unittest.TestCase):
         self.assertEqual(slice(None,  None, -1).indices(10), (9, -1, -1))
         self.assertEqual(slice(None,  None, -2).indices(10), (9, -1, -2))
         self.assertEqual(slice(3,     None, -2).indices(10), (3, -1, -2))
+        # issue 3004 tests
+        self.assertEqual(slice(None, -9).indices(10), (0, 1, 1))
+        self.assertEqual(slice(None, -10).indices(10), (0, 0, 1))
+        self.assertEqual(slice(None, -11).indices(10), (0, 0, 1))
+        self.assertEqual(slice(None, -10, -1).indices(10), (9, 0, -1))
+        self.assertEqual(slice(None, -11, -1).indices(10), (9, -1, -1))
+        self.assertEqual(slice(None, -12, -1).indices(10), (9, -1, -1))
+        self.assertEqual(slice(None, 9).indices(10), (0, 9, 1))
+        self.assertEqual(slice(None, 10).indices(10), (0, 10, 1))
+        self.assertEqual(slice(None, 11).indices(10), (0, 10, 1))
+        self.assertEqual(slice(None, 8, -1).indices(10), (9, 8, -1))
+        self.assertEqual(slice(None, 9, -1).indices(10), (9, 9, -1))
+        self.assertEqual(slice(None, 10, -1).indices(10), (9, 9, -1))
+
         self.assertEqual(
             slice(-100,  100     ).indices(10),
             slice(None).indices(10)

Misc/NEWS

@@ -10,6 +10,13 @@ What's New in Python 2.6 beta 2?
 Core and Builtins
 -----------------
 
+- Issue #3004: Minor change to slice.indices(): the start and stop
+  arguments are now treated identically, making the behaviour easier
+  to describe and understand.  For example, slice(None, -10,
+  1).indices(9) now returns (0, 0, 1) instead of (0, -1, 1), and
+  slice(None, 10, -1).indices(10) returns (9, 9, -1) instead of (9,
+  10, -1).
+
 - Make bin() implementation parallel oct() and hex().
 
 

Objects/sliceobject.c

@@ -169,8 +169,9 @@ PySlice_GetIndicesEx(PySliceObject *r, Py_ssize_t length,
 	else {
 		if (!_PyEval_SliceIndex(r->stop, stop)) return -1;
 		if (*stop < 0) *stop += length;
-		if (*stop < 0) *stop = -1;
-		if (*stop > length) *stop = length;
+		if (*stop < 0) *stop = (*step < 0) ? -1 : 0;
+		if (*stop >= length)
+			*stop = (*step < 0) ? length - 1 : length;
 	}
 
 	if ((*step < 0 && *stop >= *start)