Rename the DimensionNames type to DimensionNamesLike. (zarr-developers#3800)

The reason for this change is the fact that the `DimensionNames` type is does not model the
actual type of the `dimension_names` attribute on the Array V3 Metadata class, but rather a
wider input type that is ultimately narrowed to that actual type. For this reason, it should
use the same `XLike` name convention as the other wide input types that get narrowed to a more
restricted type.

Author: d-v-b

src/zarr/api/asynchronous.py

@@ -24,7 +24,7 @@
 from zarr.core.common import (
     JSON,
     AccessModeLiteral,
-    DimensionNames,
+    DimensionNamesLike,
     MemoryOrder,
     ZarrFormat,
     _default_zarr_format,
@@ -914,7 +914,7 @@ async def create(
         | None
     ) = None,
     codecs: Iterable[Codec | dict[str, JSON]] | None = None,
-    dimension_names: DimensionNames = None,
+    dimension_names: DimensionNamesLike = None,
     storage_options: dict[str, Any] | None = None,
     config: ArrayConfigLike | None = None,
     **kwargs: Any,

src/zarr/api/synchronous.py

@@ -33,7 +33,7 @@
     from zarr.core.common import (
         JSON,
         AccessModeLiteral,
-        DimensionNames,
+        DimensionNamesLike,
         MemoryOrder,
         ShapeLike,
         ZarrFormat,
@@ -649,7 +649,7 @@ def create(
         | None
     ) = None,
     codecs: Iterable[Codec | dict[str, JSON]] | None = None,
-    dimension_names: DimensionNames = None,
+    dimension_names: DimensionNamesLike = None,
     storage_options: dict[str, Any] | None = None,
     config: ArrayConfigLike | None = None,
     **kwargs: Any,
@@ -832,7 +832,7 @@ def create_array(
     zarr_format: ZarrFormat | None = 3,
     attributes: dict[str, JSON] | None = None,
     chunk_key_encoding: ChunkKeyEncodingLike | None = None,
-    dimension_names: DimensionNames = None,
+    dimension_names: DimensionNamesLike = None,
     storage_options: dict[str, Any] | None = None,
     overwrite: bool = False,
     config: ArrayConfigLike | None = None,
@@ -1003,7 +1003,7 @@ def from_array(
     zarr_format: ZarrFormat | None = None,
     attributes: dict[str, JSON] | None = None,
     chunk_key_encoding: ChunkKeyEncodingLike | None = None,
-    dimension_names: DimensionNames = None,
+    dimension_names: DimensionNamesLike = None,
     storage_options: dict[str, Any] | None = None,
     overwrite: bool = False,
     config: ArrayConfigLike | None = None,

src/zarr/core/array.py

@@ -53,7 +53,7 @@
     ZARR_JSON,
     ZARRAY_JSON,
     ZATTRS_JSON,
-    DimensionNames,
+    DimensionNamesLike,
     MemoryOrder,
     ShapeLike,
     ZarrFormat,
@@ -389,7 +389,7 @@ async def create(
             | None
         ) = None,
         codecs: Iterable[Codec | dict[str, JSON]] | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         # runtime
         overwrite: bool = False,
         data: npt.ArrayLike | None = None,
@@ -417,7 +417,7 @@ async def create(
             | None
         ) = None,
         codecs: Iterable[Codec | dict[str, JSON]] | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         # runtime
         overwrite: bool = False,
         data: npt.ArrayLike | None = None,
@@ -445,7 +445,7 @@ async def create(
             | None
         ) = None,
         codecs: Iterable[Codec | dict[str, JSON]] | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         # v2 only
         chunks: ShapeLike | None = None,
         dimension_separator: Literal[".", "/"] | None = None,
@@ -479,7 +479,7 @@ async def create(
             | None
         ) = None,
         codecs: Iterable[Codec | dict[str, JSON]] | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         # v2 only
         chunks: ShapeLike | None = None,
         dimension_separator: Literal[".", "/"] | None = None,
@@ -630,7 +630,7 @@ async def _create(
             | None
         ) = None,
         codecs: Iterable[Codec | dict[str, JSON]] | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         # v2 only
         chunks: ShapeLike | None = None,
         dimension_separator: Literal[".", "/"] | None = None,
@@ -742,7 +742,7 @@ def _create_metadata_v3(
         fill_value: Any | None = DEFAULT_FILL_VALUE,
         chunk_key_encoding: ChunkKeyEncodingLike | None = None,
         codecs: Iterable[Codec | dict[str, JSON]] | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         attributes: dict[str, JSON] | None = None,
     ) -> ArrayV3Metadata:
         """
@@ -803,7 +803,7 @@ async def _create_v3(
             | None
         ) = None,
         codecs: Iterable[Codec | dict[str, JSON]] | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         attributes: dict[str, JSON] | None = None,
         overwrite: bool = False,
     ) -> AsyncArrayV3:
@@ -1998,7 +1998,7 @@ def create(
             | None
         ) = None,
         codecs: Iterable[Codec | dict[str, JSON]] | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         # v2 only
         chunks: tuple[int, ...] | None = None,
         dimension_separator: Literal[".", "/"] | None = None,
@@ -2142,7 +2142,7 @@ def _create(
             | None
         ) = None,
         codecs: Iterable[Codec | dict[str, JSON]] | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         # v2 only
         chunks: tuple[int, ...] | None = None,
         dimension_separator: Literal[".", "/"] | None = None,
@@ -4266,7 +4266,7 @@ async def from_array(
     zarr_format: ZarrFormat | None = None,
     attributes: dict[str, JSON] | None = None,
     chunk_key_encoding: ChunkKeyEncodingLike | None = None,
-    dimension_names: DimensionNames = None,
+    dimension_names: DimensionNamesLike = None,
     storage_options: dict[str, Any] | None = None,
     overwrite: bool = False,
     config: ArrayConfigLike | None = None,
@@ -4535,7 +4535,7 @@ async def init_array(
     zarr_format: ZarrFormat | None = 3,
     attributes: dict[str, JSON] | None = None,
     chunk_key_encoding: ChunkKeyEncodingLike | None = None,
-    dimension_names: DimensionNames = None,
+    dimension_names: DimensionNamesLike = None,
     overwrite: bool = False,
     config: ArrayConfigLike | None = None,
 ) -> AnyAsyncArray:
@@ -4751,7 +4751,7 @@ async def create_array(
     zarr_format: ZarrFormat | None = 3,
     attributes: dict[str, JSON] | None = None,
     chunk_key_encoding: ChunkKeyEncodingLike | None = None,
-    dimension_names: DimensionNames = None,
+    dimension_names: DimensionNamesLike = None,
     storage_options: dict[str, Any] | None = None,
     overwrite: bool = False,
     config: ArrayConfigLike | None = None,
@@ -4935,7 +4935,7 @@ def _parse_keep_array_attr(
     order: MemoryOrder | None,
     zarr_format: ZarrFormat | None,
     chunk_key_encoding: ChunkKeyEncodingLike | None,
-    dimension_names: DimensionNames,
+    dimension_names: DimensionNamesLike,
 ) -> tuple[
     tuple[int, ...] | Literal["auto"],
     ShardsLike | None,
@@ -4946,7 +4946,7 @@ def _parse_keep_array_attr(
     MemoryOrder | None,
     ZarrFormat,
     ChunkKeyEncodingLike | None,
-    DimensionNames,
+    DimensionNamesLike,
 ]:
     if isinstance(data, Array):
         if chunks == "keep":

src/zarr/core/common.py

@@ -47,7 +47,8 @@
 MemoryOrder = Literal["C", "F"]
 AccessModeLiteral = Literal["r", "r+", "a", "w", "w-"]
 ANY_ACCESS_MODE: Final = "r", "r+", "a", "w", "w-"
-DimensionNames = Iterable[str | None] | None
+DimensionNamesLike = Iterable[str | None] | None
+DimensionNames = DimensionNamesLike  # for backwards compatibility
 
 TName = TypeVar("TName", bound=str)
 TConfig = TypeVar("TConfig", bound=Mapping[str, object])

src/zarr/core/group.py

@@ -40,7 +40,7 @@
     ZATTRS_JSON,
     ZGROUP_JSON,
     ZMETADATA_V2_JSON,
-    DimensionNames,
+    DimensionNamesLike,
     NodeType,
     ShapeLike,
     ZarrFormat,
@@ -1032,7 +1032,7 @@ async def create_array(
         order: MemoryOrder | None = None,
         attributes: dict[str, JSON] | None = None,
         chunk_key_encoding: ChunkKeyEncodingLike | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         storage_options: dict[str, Any] | None = None,
         overwrite: bool = False,
         config: ArrayConfigLike | None = None,
@@ -2483,7 +2483,7 @@ def create(
         order: MemoryOrder | None = None,
         attributes: dict[str, JSON] | None = None,
         chunk_key_encoding: ChunkKeyEncodingLike | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         storage_options: dict[str, Any] | None = None,
         overwrite: bool = False,
         config: ArrayConfigLike | None = None,
@@ -2627,7 +2627,7 @@ def create_array(
         order: MemoryOrder | None = None,
         attributes: dict[str, JSON] | None = None,
         chunk_key_encoding: ChunkKeyEncodingLike | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         storage_options: dict[str, Any] | None = None,
         overwrite: bool = False,
         config: ArrayConfigLike | None = None,
@@ -3025,7 +3025,7 @@ def array(
         order: MemoryOrder | None = None,
         attributes: dict[str, JSON] | None = None,
         chunk_key_encoding: ChunkKeyEncodingLike | None = None,
-        dimension_names: DimensionNames = None,
+        dimension_names: DimensionNamesLike = None,
         storage_options: dict[str, Any] | None = None,
         overwrite: bool = False,
         config: ArrayConfigLike | None = None,

src/zarr/core/metadata/v3.py

@@ -33,7 +33,7 @@
 from zarr.core.common import (
     JSON,
     ZARR_JSON,
-    DimensionNames,
+    DimensionNamesLike,
     NamedConfig,
     parse_named_configuration,
     parse_shapelike,
@@ -220,7 +220,7 @@ def __init__(
         fill_value: object,
         codecs: Iterable[Codec | dict[str, JSON] | NamedConfig[str, Any] | str],
         attributes: dict[str, JSON] | None,
-        dimension_names: DimensionNames,
+        dimension_names: DimensionNamesLike,
         storage_transformers: Iterable[dict[str, JSON]] | None = None,
         extra_fields: Mapping[str, AllowedExtraField] | None = None,
     ) -> None:

test_repro.py

@@ -0,0 +1,50 @@
+import asyncio
+import zarr
+
+async def list_prefix(store, prefix):
+    return sorted([k async for k in store.list_prefix(prefix)])
+
+async def run():
+    print("\n=== Testing with actual data ===")
+    
+    # Create memory store
+    print("\nMemoryStore:")
+    store_mem = zarr.storage.MemoryStore()
+    root_mem = zarr.open_group(store_mem, mode="w")
+    root_mem.create_group("0")
+    root_mem.create_array("0_c", shape=(1,), dtype="i4")
+    result = await list_prefix(store_mem, "0")
+    print(f"  list_prefix('0'): {result}")
+    
+    # Also print all keys
+    all_keys = sorted([k async for k in store_mem.list()])
+    print(f"  all keys: {all_keys}")
+    
+    # Create local store
+    print("\nLocalStore:")
+    import shutil
+    import tempfile
+    tmpdir = tempfile.mkdtemp()
+    store_local = zarr.storage.LocalStore(root=tmpdir)
+    root_local = zarr.open_group(store_local, mode="w")
+    root_local.create_group("0")
+    root_local.create_array("0_c", shape=(1,), dtype="i4")
+    result = await list_prefix(store_local, "0")
+    print(f"  list_prefix('0'): {result}")
+    
+    # Also print all keys
+    all_keys = sorted([k async for k in store_local.list()])
+    print(f"  all keys: {all_keys}")
+    
+    # Cleanup
+    shutil.rmtree(tmpdir)
+    
+    print("\n=== The Issue ===")
+    print("When calling list_prefix('0'):")
+    print("- MemoryStore returns both '0/zarr.json' and '0_c/zarr.json'")
+    print("- LocalStore returns only '0/zarr.json'")
+    print("\nThe divergence is in how they interpret the prefix:")
+    print("- MemoryStore: Uses string.startswith() which matches '0_c' because it starts with '0'")
+    print("- LocalStore: Treats '0' as a directory path, so it doesn't match '0_c'")
+
+asyncio.run(run())

tests/conftest.py

@@ -25,7 +25,7 @@
 from zarr.core.chunk_grids import RegularChunkGrid, _auto_partition
 from zarr.core.common import (
     JSON,
-    DimensionNames,
+    DimensionNamesLike,
     MemoryOrder,
     ShapeLike,
     ZarrFormat,
@@ -313,7 +313,7 @@ def create_array_metadata(
     zarr_format: ZarrFormat,
     attributes: dict[str, JSON] | None = None,
     chunk_key_encoding: ChunkKeyEncoding | ChunkKeyEncodingLike | None = None,
-    dimension_names: DimensionNames = None,
+    dimension_names: DimensionNamesLike = None,
 ) -> ArrayV2Metadata | ArrayV3Metadata:
     """
     Create array metadata
@@ -452,7 +452,7 @@ def meta_from_array(
     zarr_format: ZarrFormat = 3,
     attributes: dict[str, JSON] | None = None,
     chunk_key_encoding: ChunkKeyEncoding | ChunkKeyEncodingLike | None = None,
-    dimension_names: DimensionNames = None,
+    dimension_names: DimensionNamesLike = None,
 ) -> ArrayV3Metadata | ArrayV2Metadata:
     """
     Create array metadata from an array

tests/core/test_array_scalar_indexing.py

@@ -0,0 +1,57 @@
+"""Tests for scalar indexing (Issue #3741)."""
+
+import numpy as np
+import pytest
+
+import zarr
+
+
+class TestScalarIndexing:
+    """Test that scalar indexing returns numpy scalars, matching numpy behavior."""
+
+    def test_1d_scalar_indexing(self):
+        """Test scalar indexing on 1-D array returns numpy scalar."""
+        arr_zarr = zarr.array([1, 2, 3, 4, 5], dtype="int64")
+        arr_numpy = np.array([1, 2, 3, 4, 5], dtype="int64")
+
+        result_zarr = arr_zarr[0]
+        result_numpy = arr_numpy[0]
+
+        assert type(result_zarr) == type(result_numpy)
+        assert result_zarr == result_numpy
+        assert not isinstance(result_zarr, np.ndarray)
+        assert isinstance(result_zarr, np.generic)
+
+    def test_2d_scalar_indexing(self):
+        """Test scalar indexing on 2-D array returns numpy scalar."""
+        arr_zarr = zarr.array([[1, 2, 3], [4, 5, 6]], dtype="int64")
+        arr_numpy = np.array([[1, 2, 3], [4, 5, 6]], dtype="int64")
+
+        result_zarr = arr_zarr[0, 0]
+        result_numpy = arr_numpy[0, 0]
+
+        assert type(result_zarr) == type(result_numpy)
+        assert result_zarr == result_numpy
+        assert not isinstance(result_zarr, np.ndarray)
+
+    def test_slice_indexing_returns_array(self):
+        """Test that slice indexing still returns arrays."""
+        arr_zarr = zarr.array([1, 2, 3, 4, 5])
+        result = arr_zarr[0:2]
+
+        assert isinstance(result, np.ndarray)
+        assert result.ndim == 1
+        assert len(result) == 2
+
+    def test_partial_scalar_indexing_on_2d(self):
+        """Test partial scalar indexing on 2-D array returns 1-D array."""
+        arr_zarr = zarr.array([[1, 2, 3], [4, 5, 6]], dtype="int64")
+        arr_numpy = np.array([[1, 2, 3], [4, 5, 6]], dtype="int64")
+
+        result_zarr = arr_zarr[0]
+        result_numpy = arr_numpy[0]
+
+        assert type(result_zarr) == type(result_numpy)
+        assert isinstance(result_zarr, np.ndarray)
+        assert result_zarr.ndim == 1
+        np.testing.assert_array_equal(result_zarr, result_numpy)