Fix: Infinite loop over index.keys

Closes #544

Co-authored-by: Mobin Larijanian <22958029+mobinln@users.noreply.github.com>

Author: ashvardanian

python/scripts/test_index.py

@@ -403,6 +403,16 @@ def test_index_clustering(ndim, metric, quantization, dtype, batch_size):
     assert len(unique_clusters) >= 3 and len(unique_clusters) <= 10
 
 
+def test_index_keys_iteration():
+    """Test that iterating over index.keys works without infinite loop."""
+    index = Index(ndim=3)
+    index.add(keys=[42], vectors=np.array([0.2, 0.3, 0.5]))
+    
+    keys_list = list(index.keys)
+    assert len(keys_list) == 1
+    assert keys_list[0] == 42
+
+
 def test_index_copied_memory_usage():
     """Test that copy=False results in lower memory usage than copy=True."""
     reset_randomness()

python/usearch/index.py

@@ -459,8 +459,8 @@ def __getitem__(
     ) -> Union[Key, np.ndarray]:
         if isinstance(offset_offsets_or_slice, slice):
             start, stop, step = offset_offsets_or_slice.indices(len(self))
-            if step:
-                raise
+            if step != 1:
+                raise ValueError("Slicing with a step is not supported")
             return self.index._compiled.get_keys_in_slice(start, stop - start)
 
         elif isinstance(offset_offsets_or_slice, Iterable):
@@ -469,6 +469,10 @@ def __getitem__(
 
         else:
             offset = int(offset_offsets_or_slice)
+            if offset < 0:
+                offset += len(self)
+            if offset < 0 or offset >= len(self):
+                raise IndexError("Index out of range")
             return self.index._compiled.get_key_at_offset(offset)
 
     def __array__(self, dtype=None) -> np.ndarray: