Make chunk manager an option in set_options (pydata#9362)

* Make chunk manager an option in `set_options`

* Add docs

* Add unit test

* Add what's new entry

Author: tomwhite

doc/internals/chunked-arrays.rst

@@ -91,7 +91,8 @@ Once the chunkmanager subclass has been registered, xarray objects wrapping the
 The latter two methods ultimately call the chunkmanager's implementation of ``.from_array``, to which they pass the ``from_array_kwargs`` dict.
 The ``chunked_array_type`` kwarg selects which registered chunkmanager subclass to dispatch to. It defaults to ``'dask'``
 if Dask is installed, otherwise it defaults to whichever chunkmanager is registered if only one is registered.
-If multiple chunkmanagers are registered it will raise an error by default.
+If multiple chunkmanagers are registered, the ``chunk_manager`` configuration option (which can be set using :py:func:`set_options`)
+will be used to determine which chunkmanager to use, defaulting to ``'dask'``.
 
 Parallel processing without chunks
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

doc/whats-new.rst

@@ -22,7 +22,8 @@ v2024.07.1 (unreleased)
 
 New Features
 ~~~~~~~~~~~~
-
+- Make chunk manager an option in ``set_options`` (:pull:`9362`).
+  By `Tom White <https://github.com/tomwhite>`_.
 
 Breaking changes
 ~~~~~~~~~~~~~~~~

xarray/core/options.py

@@ -10,6 +10,7 @@
 
     Options = Literal[
         "arithmetic_join",
+        "chunk_manager",
         "cmap_divergent",
         "cmap_sequential",
         "display_max_rows",
@@ -36,6 +37,7 @@
     class T_Options(TypedDict):
         arithmetic_broadcast: bool
         arithmetic_join: Literal["inner", "outer", "left", "right", "exact"]
+        chunk_manager: str
         cmap_divergent: str | Colormap
         cmap_sequential: str | Colormap
         display_max_rows: int
@@ -62,6 +64,7 @@ class T_Options(TypedDict):
 OPTIONS: T_Options = {
     "arithmetic_broadcast": True,
     "arithmetic_join": "inner",
+    "chunk_manager": "dask",
     "cmap_divergent": "RdBu_r",
     "cmap_sequential": "viridis",
     "display_max_rows": 12,
@@ -172,7 +175,9 @@ class set_options:
         - "override": if indexes are of same size, rewrite indexes to be
           those of the first object with that dimension. Indexes for the same
           dimension must have the same size in all objects.
-
+    chunk_manager : str, default: "dask"
+        Chunk manager to use for chunked array computations when multiple
+        options are installed.
     cmap_divergent : str or matplotlib.colors.Colormap, default: "RdBu_r"
         Colormap to use for divergent data plots. If string, must be
         matplotlib built-in colormap. Can also be a Colormap object

xarray/namedarray/parallelcompat.py

@@ -14,6 +14,7 @@
 
 import numpy as np
 
+from xarray.core.options import OPTIONS
 from xarray.core.utils import emit_user_level_warning
 from xarray.namedarray.pycompat import is_chunked_array
 
@@ -101,8 +102,8 @@ def guess_chunkmanager(
             # use the only option available
             manager = next(iter(chunkmanagers.keys()))
         else:
-            # default to trying to use dask
-            manager = "dask"
+            # use the one in options (default dask)
+            manager = OPTIONS["chunk_manager"]
 
     if isinstance(manager, str):
         if manager not in chunkmanagers:

xarray/tests/test_parallelcompat.py

@@ -6,6 +6,7 @@
 import numpy as np
 import pytest
 
+from xarray import set_options
 from xarray.core.types import T_Chunks, T_DuckArray, T_NormalizedChunks
 from xarray.namedarray._typing import _Chunks
 from xarray.namedarray.daskmanager import DaskManager
@@ -152,6 +153,11 @@ def test_get_chunkmanger(self, register_dummy_chunkmanager) -> None:
         chunkmanager = guess_chunkmanager("dummy")
         assert isinstance(chunkmanager, DummyChunkManager)
 
+    def test_get_chunkmanger_via_set_options(self, register_dummy_chunkmanager) -> None:
+        with set_options(chunk_manager="dummy"):
+            chunkmanager = guess_chunkmanager(None)
+            assert isinstance(chunkmanager, DummyChunkManager)
+
     def test_fail_on_nonexistent_chunkmanager(self) -> None:
         with pytest.raises(ValueError, match="unrecognized chunk manager foo"):
             guess_chunkmanager("foo")