Accept dictionaries for store argument (zarr-developers#2164)

* Accept dictionaries for `store`

* fixup doc build warnings

* Only support dictionaries

Author: TomAugspurger

src/zarr/api/asynchronous.py

@@ -497,8 +497,18 @@ async def open_group(
 
     Parameters
     ----------
-    store : Store or string, optional
+    store : Store, string, or mapping, optional
         Store or path to directory in file system or name of zip file.
+
+        Strings are interpreted as paths on the local file system
+        and used as the ``root`` argument to :class:`zarr.store.LocalStore`.
+
+        Dictionaries are used as the ``store_dict`` argument in
+        :class:`zarr.store.MemoryStore``.
+
+        By default (``store=None``) a new :class:`zarr.store.MemoryStore`
+        is created.
+
     mode : {'r', 'r+', 'a', 'w', 'w-'}, optional
         Persistence mode: 'r' means read only (must exist); 'r+' means
         read/write (must exist); 'a' means read/write (create if doesn't

src/zarr/core/buffer/core.py

@@ -195,8 +195,8 @@ def from_buffer(cls, buffer: Buffer) -> Self:
         -------
             A new buffer representing the content of the input buffer
 
-        Note
-        ----
+        Notes
+        -----
         Subclasses of `Buffer` must override this method to implement
         more optimal conversions that avoid copies where possible
         """

src/zarr/core/buffer/cpu.py

@@ -73,8 +73,8 @@ def from_buffer(cls, buffer: core.Buffer) -> Self:
         -------
             A new buffer representing the content of the input buffer
 
-        Note
-        ----
+        Notes
+        -----
         Subclasses of `Buffer` must override this method to implement
         more optimal conversions that avoid copies where possible
         """

src/zarr/core/buffer/gpu.py

@@ -38,8 +38,8 @@ class Buffer(core.Buffer):
     array-like instance can be copied/converted to a regular Numpy array
     (host memory).
 
-    Note
-    ----
+    Notes
+    -----
     This buffer is untyped, so all indexing and sizes are in bytes.
 
     Parameters
@@ -123,8 +123,8 @@ class NDBuffer(core.NDBuffer):
     ndarray-like instance can be copied/converted to a regular Numpy array
     (host memory).
 
-    Note
-    ----
+    Notes
+    -----
     The two buffer classes Buffer and NDBuffer are very similar. In fact, Buffer
     is a special case of NDBuffer where dim=1, stride=1, and dtype="b". However,
     in order to use Python's type system to differentiate between the contiguous
@@ -193,8 +193,8 @@ def from_numpy_array(cls, array_like: npt.ArrayLike) -> Self:
     def as_numpy_array(self) -> npt.NDArray[Any]:
         """Returns the buffer as a NumPy array (host memory).
 
-        Warning
-        -------
+        Warnings
+        --------
         Might have to copy data, consider using `.as_ndarray_like()` instead.
 
         Returns

src/zarr/store/common.py

@@ -71,7 +71,7 @@ def __eq__(self, other: Any) -> bool:
         return False
 
 
-StoreLike = Store | StorePath | Path | str
+StoreLike = Store | StorePath | Path | str | dict[str, Buffer]
 
 
 async def make_store_path(
@@ -94,6 +94,10 @@ async def make_store_path(
         return StorePath(await LocalStore.open(root=store_like, mode=mode or "r"))
     elif isinstance(store_like, str):
         return StorePath(await LocalStore.open(root=Path(store_like), mode=mode or "r"))
+    elif isinstance(store_like, dict):
+        # We deliberate only consider dict[str, Buffer] here, and not arbitrary mutable mappings.
+        # By only allowing dictionaries, which are in-memory, we know that MemoryStore appropriate.
+        return StorePath(await MemoryStore.open(store_dict=store_like, mode=mode))
     raise TypeError
 
 

tests/v3/test_group.py

@@ -5,7 +5,9 @@
 import numpy as np
 import pytest
 
+import zarr.api.asynchronous
 from zarr import Array, AsyncArray, AsyncGroup, Group
+from zarr.api.synchronous import open_group
 from zarr.core.buffer import default_buffer_prototype
 from zarr.core.common import ZarrFormat
 from zarr.core.group import GroupMetadata
@@ -820,3 +822,13 @@ async def test_require_array(store: LocalStore | MemoryStore, zarr_format: ZarrF
     _ = await root.create_group("bar")
     with pytest.raises(TypeError, match="Incompatible object"):
         await root.require_array("bar", shape=(10,), dtype="int8")
+
+
+async def test_open_mutable_mapping():
+    group = await zarr.api.asynchronous.open_group(store={}, mode="w")
+    assert isinstance(group.store_path.store, MemoryStore)
+
+
+def test_open_mutable_mapping_sync():
+    group = open_group(store={}, mode="w")
+    assert isinstance(group.store_path.store, MemoryStore)