Special case object dtype

Closes zarr-developers#2315

src/zarr/core/array.py

@@ -35,6 +35,7 @@
     ShapeLike,
     ZarrFormat,
     concurrent_map,
+    parse_dtype,
     parse_shapelike,
     product,
 )
@@ -226,7 +227,8 @@ async def create(
         if chunks is not None and chunk_shape is not None:
             raise ValueError("Only one of chunk_shape or chunks can be provided.")
 
-        dtype = np.dtype(dtype)
+        dtype = parse_dtype(dtype)
+        # dtype = np.dtype(dtype)
         if chunks:
             _chunks = normalize_chunks(chunks, shape, dtype.itemsize)
         else:

src/zarr/core/common.py

@@ -16,6 +16,8 @@
     overload,
 )
 
+import numpy as np
+
 if TYPE_CHECKING:
     from collections.abc import Awaitable, Callable, Iterator
 
@@ -162,3 +164,10 @@ def parse_order(data: Any) -> Literal["C", "F"]:
     if data in ("C", "F"):
         return cast(Literal["C", "F"], data)
     raise ValueError(f"Expected one of ('C', 'F'), got {data} instead.")
+
+
+def parse_dtype(dtype: Any) -> np.dtype[Any]:
+    if dtype is str or dtype == "str":
+        # special case as object
+        return np.dtype("object")
+    return np.dtype(dtype)

src/zarr/core/metadata/v2.py

@@ -22,7 +22,7 @@
 from zarr.core.array_spec import ArraySpec
 from zarr.core.chunk_grids import RegularChunkGrid
 from zarr.core.chunk_key_encodings import parse_separator
-from zarr.core.common import ZARRAY_JSON, ZATTRS_JSON, parse_shapelike
+from zarr.core.common import ZARRAY_JSON, ZATTRS_JSON, parse_dtype, parse_shapelike
 from zarr.core.config import config, parse_indexing_order
 from zarr.core.metadata.common import ArrayMetadata, parse_attributes
 
@@ -201,11 +201,6 @@ def update_attributes(self, attributes: dict[str, JSON]) -> Self:
         return replace(self, attributes=attributes)
 
 
-def parse_dtype(data: npt.DTypeLike) -> np.dtype[Any]:
-    # todo: real validation
-    return np.dtype(data)
-
-
 def parse_zarr_format(data: object) -> Literal[2]:
     if data == 2:
         return 2

src/zarr/core/metadata/v3.py

@@ -504,6 +504,7 @@ class DataType(Enum):
     complex128 = "complex128"
     string = "string"
     bytes = "bytes"
+    object = "object"
 
     @property
     def byte_count(self) -> None | int:
@@ -549,6 +550,7 @@ def to_numpy_shortname(self) -> str:
             DataType.float64: "f8",
             DataType.complex64: "c8",
             DataType.complex128: "c16",
+            DataType.object: "object",
         }
         return data_type_to_numpy[self]
 
@@ -572,6 +574,8 @@ def from_numpy(cls, dtype: np.dtype[Any]) -> DataType:
             return DataType.string
         elif dtype.kind == "S":
             return DataType.bytes
+        elif dtype.kind == "O":
+            return DataType.object
         dtype_to_data_type = {
             "|b1": "bool",
             "bool": "bool",

tests/v3/test_array.py

@@ -1,6 +1,6 @@
 import pickle
 from itertools import accumulate
-from typing import Literal
+from typing import Any, Literal
 
 import numpy as np
 import pytest
@@ -406,3 +406,10 @@ def test_vlen_errors() -> None:
             dtype="<U4",
             codecs=[BytesCodec(), VLenBytesCodec()],
         )
+
+
+@pytest.mark.parametrize("zarr_format", [2, 3, None])
+@pytest.mark.parametrize("dtype", [str, "str"])
+def test_create_dtype_str(dtype: Any, zarr_format: ZarrFormat | None) -> None:
+    arr = zarr.create(shape=10, dtype=dtype, zarr_format=zarr_format)
+    assert arr.dtype.kind == "O"