Set object codec for object arrays

cubed/storage/backend.py

@@ -4,16 +4,7 @@
 from cubed.types import T_DType, T_RegularChunks, T_Shape, T_Store
 
 
-def open_backend_array(
-    store: T_Store,
-    mode: str,
-    *,
-    shape: Optional[T_Shape] = None,
-    dtype: Optional[T_DType] = None,
-    chunks: Optional[T_RegularChunks] = None,
-    path: Optional[str] = None,
-    **kwargs,
-):
+def backend_storage_name():
     # get storage name from top-level config
     # e.g. set globally with CUBED_STORAGE_NAME=tensorstore
     storage_name = config.get("storage_name", None)
@@ -26,10 +17,35 @@ def open_backend_array(
         else:
             storage_name = "zarr-python"
 
+    return storage_name
+
+
+def open_backend_array(
+    store: T_Store,
+    mode: str,
+    *,
+    shape: Optional[T_Shape] = None,
+    dtype: Optional[T_DType] = None,
+    chunks: Optional[T_RegularChunks] = None,
+    path: Optional[str] = None,
+    **kwargs,
+):
+    storage_name = backend_storage_name()
+
     if storage_name == "zarr-python":
         from cubed.storage.backends.zarr_python import open_zarr_array
 
         open_func = open_zarr_array
+
+        # set object codec if needed
+        import numpy as np
+
+        if np.dtype(dtype).hasobject and "object_codec" not in kwargs:
+            import numcodecs
+
+            object_codec = numcodecs.Pickle()
+            kwargs["object_codec"] = object_codec
+
     elif storage_name == "zarr-python-v3":
         from cubed.storage.backends.zarr_python_v3 import open_zarr_v3_array
 

cubed/tests/test_types.py

@@ -1,10 +1,22 @@
+import pytest
 from numpy.testing import assert_array_equal
 
+import cubed
 import cubed.array_api as xp
+from cubed.storage.backend import backend_storage_name
 
 
 # This is less strict than the spec, but is supported by implementations like NumPy
 def test_prod_sum_bool():
     a = xp.ones((2,), dtype=xp.bool)
     assert_array_equal(xp.prod(a).compute(), xp.asarray([1], dtype=xp.int64))
     assert_array_equal(xp.sum(a).compute(), xp.asarray([2], dtype=xp.int64))
+
+
+@pytest.mark.skipif(
+    backend_storage_name() != "zarr-python",
+    reason="object dtype only works on zarr-python",
+)
+def test_object_dtype():
+    a = xp.asarray(["a", "b"], dtype=object, chunks=2)
+    cubed.to_zarr(a, store=None)