zarr.open should fall back to opening a group

Closes #2309

Author: TomAugspurger

src/zarr/api/asynchronous.py

@@ -247,7 +247,10 @@ async def open(
 
     try:
         return await open_array(store=store_path, zarr_format=zarr_format, **kwargs)
-    except KeyError:
+    except (KeyError, ValueError):
+        # KeyError for a missing key
+        # ValueError for failing to parse node metadata as an array when it's
+        # actually a group
         return await open_group(store=store_path, zarr_format=zarr_format, **kwargs)
 
 
@@ -580,6 +583,8 @@ async def open_group(
     meta_array : array-like, optional
         An array instance to use for determining arrays to create and return
         to users. Use `numpy.empty(())` by default.
+    attributes : dict
+        A dictionary of JSON-serializable values with user-defined attributes.
 
     Returns
     -------

src/zarr/api/synchronous.py

@@ -207,6 +207,7 @@ def open_group(
     zarr_version: ZarrFormat | None = None,  # deprecated
     zarr_format: ZarrFormat | None = None,
     meta_array: Any | None = None,  # not used in async api
+    attributes: dict[str, JSON] | None = None,
 ) -> Group:
     return Group(
         sync(
@@ -221,6 +222,7 @@ def open_group(
                 zarr_version=zarr_version,
                 zarr_format=zarr_format,
                 meta_array=meta_array,
+                attributes=attributes,
             )
         )
     )

tests/v3/test_api.py

@@ -6,6 +6,7 @@
 from numpy.testing import assert_array_equal
 
 import zarr
+import zarr.api.asynchronous
 from zarr import Array, Group
 from zarr.abc.store import Store
 from zarr.api.synchronous import create, group, load, open, open_group, save, save_array, save_group
@@ -921,3 +922,23 @@ def test_open_group_positional_args_deprecated() -> None:
     store = MemoryStore({}, mode="w")
     with pytest.warns(FutureWarning, match="pass"):
         open_group(store, "w")
+
+
+def test_open_falls_back_to_open_group() -> None:
+    # https://github.com/zarr-developers/zarr-python/issues/2309
+    store = MemoryStore(mode="w")
+    zarr.open_group(store, attributes={"key": "value"})
+
+    group = zarr.open(store)
+    assert isinstance(group, Group)
+    assert group.attrs == {"key": "value"}
+
+
+async def test_open_falls_back_to_open_group_async() -> None:
+    # https://github.com/zarr-developers/zarr-python/issues/2309
+    store = MemoryStore(mode="w")
+    await zarr.api.asynchronous.open_group(store, attributes={"key": "value"})
+
+    group = await zarr.api.asynchronous.open(store=store)
+    assert isinstance(group, zarr.api.asynchronous.AsyncGroup)
+    assert group.attrs == {"key": "value"}