Special case str dtype in array creation

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, zarr_format)
+        # dtype = np.dtype(dtype)
         if chunks:
             _chunks = normalize_chunks(chunks, shape, dtype.itemsize)
         else:

src/zarr/core/common.py

@@ -16,6 +16,10 @@
     overload,
 )
 
+import numpy as np
+
+from zarr.core.strings import _STRING_DTYPE
+
 if TYPE_CHECKING:
     from collections.abc import Awaitable, Callable, Iterator
 
@@ -162,3 +166,13 @@ 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, zarr_format: ZarrFormat) -> np.dtype[Any]:
+    if dtype is str or dtype == "str":
+        if zarr_format == 2:
+            # special case as object
+            return np.dtype("object")
+        else:
+            return _STRING_DTYPE
+    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
 
@@ -57,7 +57,7 @@ def __init__(
         Metadata for a Zarr version 2 array.
         """
         shape_parsed = parse_shapelike(shape)
-        data_type_parsed = parse_dtype(dtype)
+        data_type_parsed = parse_dtype(dtype, zarr_format=2)
         chunks_parsed = parse_shapelike(chunks)
         compressor_parsed = parse_compressor(compressor)
         order_parsed = parse_indexing_order(order)
@@ -141,7 +141,7 @@ def from_dict(cls, data: dict[str, Any]) -> ArrayV2Metadata:
         _data = data.copy()
         # check that the zarr_format attribute is correct
         _ = parse_zarr_format(_data.pop("zarr_format"))
-        dtype = parse_dtype(_data["dtype"])
+        dtype = parse_dtype(_data["dtype"], zarr_format=2)
 
         if dtype.kind in "SV":
             fill_value_encoded = _data.get("fill_value")
@@ -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

tests/v3/test_codecs/test_vlen.py

@@ -11,7 +11,7 @@
 from zarr.core.strings import _NUMPY_SUPPORTS_VLEN_STRING
 from zarr.storage.common import StorePath
 
-numpy_str_dtypes: list[type | None] = [None, str, np.dtypes.StrDType]
+numpy_str_dtypes: list[type | str | None] = [None, str, "str", np.dtypes.StrDType]
 expected_zarr_string_dtype: np.dtype[Any]
 if _NUMPY_SUPPORTS_VLEN_STRING:
     numpy_str_dtypes.append(np.dtypes.StringDType)

tests/v3/test_v2.py

@@ -1,5 +1,6 @@
 import json
 from collections.abc import Iterator
+from typing import Any
 
 import numpy as np
 import pytest
@@ -84,3 +85,10 @@ async def test_v2_encode_decode(dtype):
     data = zarr.open_array(store=store, path="foo")[:]
     expected = np.full((3,), b"X", dtype=dtype)
     np.testing.assert_equal(data, expected)
+
+
+@pytest.mark.parametrize("dtype", [str, "str"])
+async def test_create_dtype_str(dtype: Any) -> None:
+    arr = zarr.create(shape=10, dtype=dtype, zarr_format=2)
+    assert arr.dtype.kind == "O"
+    assert arr.metadata.to_dict()["dtype"] == "|O"