Some days, I think my comment of

	/* this is harder to get right than you might think */

angered some God somewhere.  After noticing

    >>> range(5000000)[slice(96360, None, 439)]
    []

I found that my cute test for the slice being empty failed due to
overflow.  Fixed, and added simple test (not the above!).

Author: Michael W. Hudson

Lib/test/test_slice.py

@@ -1,6 +1,7 @@
 # tests for slice objects; in particular the indices method.
 
 from test.test_support import vereq
+import sys
 
 vereq(slice(None           ).indices(10), (0, 10,  1))
 vereq(slice(None,  None,  2).indices(10), (0, 10,  2))
@@ -11,3 +12,5 @@
 vereq(slice(-100,  100     ).indices(10), slice(None).indices(10))
 vereq(slice(100,  -100,  -1).indices(10), slice(None, None, -1).indices(10))
 vereq(slice(-100L, 100L, 2L).indices(10), (0, 10,  2))
+
+vereq(range(10)[::sys.maxint - 1], [0])

Objects/sliceobject.c

@@ -114,11 +114,13 @@ PySlice_GetIndicesEx(PySliceObject *r, int length,
 		     int *start, int *stop, int *step, int *slicelength)
 {
 	/* this is harder to get right than you might think */
+
 	int defstart, defstop;
 
 	if (r->step == Py_None) {
 		*step = 1;
-	} else {
+	} 
+	else {
 		*step = PyInt_AsLong(r->step);
 		if (*step == -1 && PyErr_Occurred()) {
 			return -1;
@@ -135,7 +137,8 @@ PySlice_GetIndicesEx(PySliceObject *r, int length,
 
 	if (r->start == Py_None) {
 		*start = defstart;
-	} else {
+	}
+	else {
 		if (!_PyEval_SliceIndex(r->start, start)) return -1;
 		if (*start < 0) *start += length;
 		if (*start < 0) *start = (*step < 0) ? -1 : 0;
@@ -145,19 +148,22 @@ PySlice_GetIndicesEx(PySliceObject *r, int length,
 
 	if (r->stop == Py_None) {
 		*stop = defstop;
-	} else {
+	}
+	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 - *start)*(*step) <= 0) {
+
+	if ((*step < 0 && *stop >= *start) 
+	    || (*step > 0 && *start >= *stop)) {
 		*slicelength = 0;
 	}
 	else if (*step < 0) {
 		*slicelength = (*stop-*start+1)/(*step)+1;
-	} else {
+	}
+	else {
 		*slicelength = (*stop-*start-1)/(*step)+1;
 	}