Fix Count and Range __getitem__ methods. (#76)

These were wrong for slices and negative indices. These are now fixed
and tested.

Fixes #75

src/tempe/data_view.py

@@ -278,8 +278,8 @@ def __len__(self):
     def __getitem__(self, index):
         if isinstance(index, slice):
             return [
-                self.start + self.step * index
-                for index in range(slice.start, slice.stop, slice, step)
+                self.start + self.step * i
+                for i in range(index.start, index.stop, index.step)
             ]
         else:
             return self.start + self.step * index
@@ -305,11 +305,13 @@ def __len__(self):
     def __getitem__(self, index):
         if isinstance(index, slice):
             return [
-                self.start + self.step * self.index
-                for index in range(slice.start, slice.stop, slice, step)
+                self.start + self.step * i
+                for i in range(index.start, index.stop, index.step)
             ]
-        else:
-            return self.start + self.step * self.index
+        elif index < 0:
+            index = len(self) + index
+
+        return self.start + self.step * index
 
 
 class Slice(DataView):

tests/tempe/test_data_views.py

@@ -4,7 +4,7 @@
 
 import unittest
 
-from tempe.data_view import Count
+from tempe.data_view import Count, Range
 
 
 class TestCount(unittest.TestCase):
@@ -27,6 +27,15 @@ def test_count_getitem(self):
         self.assertEqual(count[0], 10)
         self.assertEqual(count[1], 15)
         self.assertEqual(count[2], 20)
+        # consistent, so leave it as behaviour
+        self.assertEqual(count[-1], 5)
+
+    def test_count_getitem_slice(self):
+        """Test count getitem works with slices."""
+
+        count = Count(10, 5)
+
+        self.assertEqual(count[2:5:2], [20, 30])
 
     def test_count_default(self):
         """Test count default starts and steps as expected."""
@@ -48,6 +57,49 @@ def test_count_default_getitem(self):
         self.assertEqual(count[2], 2)
 
 
+class TestRange(unittest.TestCase):
+
+    def test_range(self):
+        """Test range starts and steps as expected."""
+
+        r = Range(10, 25, 5)
+
+        self.assertEqual(list(r), [10, 15, 20])
+
+    def test_range_len(self):
+        """Test range length is correct."""
+
+        r = Range(10, 25, 5)
+
+        self.assertEqual(len(r), 3)
+
+    def test_range_getitem(self):
+        """Test range getitem works as expected."""
+
+        r = Range(10, 25, 5)
+
+        self.assertEqual(r[0], 10)
+        self.assertEqual(r[1], 15)
+        self.assertEqual(r[2], 20)
+        self.assertEqual(r[-1], 20)
+
+    def test_range_getitem_slice(self):
+        """Test range getitem works with slices."""
+
+        r = Range(10, 50, 5)
+
+        self.assertEqual(r[2:5:2], [20, 30])
+
+    def test_range_defaults(self):
+        """Test range default starts and steps as expected."""
+
+        r1 = Range(10)
+        r2 = Range(10, 15)
+
+        self.assertEqual(list(r1), list(range(10)))
+        self.assertEqual(list(r2), list(range(10, 15)))
+
+
 if __name__ == "__main__":
     result = unittest.main()
     if not result.wasSuccessful():