Add handling of negative indices to getitem

numpy_ringbuffer/__init__.py

@@ -164,6 +164,10 @@ def __len__(self):
 	def __getitem__(self, item):
 		# handle simple (b[1]) and basic (b[np.array([1, 2, 3])]) fancy indexing specially
 		if not isinstance(item, tuple):
+			if isinstance(item, int) and item < 0:
+				# ringbuf[-<n>]
+				item = (item + self._right_index) % self._capacity
+				return self._arr[item]
 			item_arr = np.asarray(item)
 			if issubclass(item_arr.dtype.type, np.integer):
 				item_arr = (item_arr + self._left_index) % self._capacity

tests.py

@@ -58,6 +58,20 @@ def test_getitem(self):
 		ii = [0, 4, 3, 1, 2]
 		np.testing.assert_equal(r[ii], expected[ii])
 
+	def test_getitem_from_right(self):
+		r = RingBuffer(5, dtype=int)
+		r.append(1)
+		for num in range(2, 5):
+			r.append(num)
+			self.assertEqual(r[-1], num)
+		for num in range(5, 13):
+			r.append(num)
+			self.assertEqual(r[-1], num)
+			self.assertEqual(r[-2], num - 1)
+			self.assertEqual(r[-5], num - 4)
+		np.testing.assert_equal(r[-4:], [9, 10, 11, 12])
+		np.testing.assert_equal(r[-5:-2], [8, 9, 10])
+
 	def test_appendleft(self):
 		r = RingBuffer(5)