Bug fix for region slices that have start or stop = None

cubed/core/ops.py

@@ -212,11 +212,16 @@ def _store_array(
         shape = target.shape
         chunks = target.chunks
         for i, (sl, cs) in enumerate(zip(region, chunks)):
-            if sl.start % cs != 0 or (sl.stop % cs != 0 and sl.stop != shape[i]):
+            if (sl.start is not None and sl.start % cs != 0) or (
+                sl.stop is not None and sl.stop % cs != 0 and sl.stop != shape[i]
+            ):
                 raise ValueError(
                     f"Region {region} does not align with target chunks {chunks}"
                 )
-        block_offsets = [sl.start // cs for sl, cs in zip(region, chunks)]
+        block_offsets = [
+            (0 if sl.start is None else sl.start // cs)
+            for sl, cs in zip(region, chunks)
+        ]
 
         def key_function(out_key):
             out_coords = out_key[1:]

cubed/tests/test_core.py

@@ -190,7 +190,13 @@ def test_to_zarr_array(tmp_path, spec, executor):
 
 def test_to_zarr_region(tmp_path, spec, executor):
     a = xp.asarray(
-        [[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12], [13, 14, 15, 16]],
+        [
+            [1, 2, 3, 4],
+            [5, 6, 7, 8],
+            [9, 10, 11, 12],
+            [13, 14, 15, 16],
+            [17, 18, 19, 20],
+        ],
         chunks=(2, 2),
         spec=spec,
     )
@@ -272,6 +278,22 @@ def test_to_zarr_region(tmp_path, spec, executor):
         ),
     )
 
+    region = (slice(None), slice(4, 5))
+    cubed.to_zarr(a[:, 0:1], z, region=region, executor=executor)
+    res = open_storage_array(store, mode="r")
+    assert_array_equal(
+        res[:],
+        np.array(
+            [
+                [1, 2, 0, 0, 1],
+                [5, 6, 0, 0, 5],
+                [1, 2, 1, 2, 9],
+                [5, 6, 5, 6, 13],
+                [0, 0, 9, 10, 17],
+            ]
+        ),
+    )
+
 
 def test_to_zarr_region_fails(tmp_path):
     a = xp.ones((4, 4), chunks=(2, 2))