newrange: fixed slices on empty ranges

Author: Brad Walker

src/future/types/newrange.py

@@ -132,7 +132,9 @@ def __getitem_slice(self, slce):
         of the sequence represented by this range.
         """
         start, stop, step = slce.indices(self._len)
-        return newrange(self[start], stop + self._start, step * self._step)
+        return newrange(self._start + self._step*start,
+                        self._start + stop,
+                        self._step * step)
 
     def __iter__(self):
         """Return an iterator which enumerates the elements of the

tests/test_future/test_range.py

@@ -19,11 +19,15 @@ def test_bool_range(self):
         self.assertFalse(range(1, 1))
         self.assertFalse(range(5, 2))
 
-    def test_equality(self):
+    def test_equality_range(self):
         self.assertEqual(range(7), range(7))
         self.assertEqual(range(0), range(1, 1))
         self.assertEqual(range(0, 10, 3), range(0, 11, 3))
 
+    def test_slice_empty_range(self):
+        self.assertEqual(range(0)[:], range(0))
+        self.assertEqual(range(0)[::-1], range(-1, -1, -1))
+
     def test_slice_range(self):
         r = range(8)
         self.assertEqual(r[:], range(8))