(fix): handle case when chunks is None

src/anndata/_io/specs/lazy_methods.py

@@ -184,8 +184,11 @@ def make_dask_chunk(block_id: tuple[int, int]):
 
 @_LAZY_REGISTRY.register_read(ZarrArray, IOSpec("array", "0.2.0"))
 def read_zarr_array(
-    elem, _reader, dataset_kwargs: Mapping[str, Any] = MappingProxyType({})
+    elem: ZarrArray,
+    _reader: Reader,
+    dataset_kwargs: Mapping[str, Any] = MappingProxyType({}),
 ):
+    chunks: tuple[int, ...] = dataset_kwargs.get("chunks", elem.chunks)
     import dask.array as da
 
-    return da.from_zarr(elem)
+    return da.from_zarr(elem, chunks=chunks)

src/anndata/_io/specs/registry.py

@@ -387,7 +387,9 @@ def read_elem_as_dask(
     -------
         DaskArray
     """
-    return Reader(_LAZY_REGISTRY).read_elem(elem, dataset_kwargs={"chunks": chunks})
+    return Reader(_LAZY_REGISTRY).read_elem(
+        elem, dataset_kwargs={"chunks": chunks} if chunks is not None else {}
+    )
 
 
 def write_elem(

tests/test_io_elementwise.py

@@ -59,7 +59,7 @@ def store(request, tmp_path) -> H5Group | ZarrGroup:
 
 
 sparse_formats = ["csr", "csc"]
-SIZE = 1000
+SIZE = 2500
 
 
 @pytest.fixture(params=sparse_formats)
@@ -235,7 +235,15 @@ def test_read_lazy_2d_dask(sparse_format, store):
 
 @pytest.mark.parametrize(
     ("n_dims", "chunks"),
-    [(1, (100,)), (1, (400,)), (2, (100, 100)), (2, (400, 400)), (2, (200, 400))],
+    [
+        (1, (100,)),
+        (1, (400,)),
+        (2, (100, 100)),
+        (2, (400, 400)),
+        (2, (200, 400)),
+        (1, None),
+        (2, None),
+    ],
 )
 def test_read_lazy_nd_dask(store, n_dims, chunks):
     arr_store = create_dense_store(store, n_dims)
@@ -269,7 +277,13 @@ def test_read_lazy_h5_cluster(sparse_format, tmp_path):
 
 @pytest.mark.parametrize(
     ("arr_type", "chunks"),
-    [("dense", (100, 100)), ("csc", (SIZE, 10)), ("csr", (10, SIZE))],
+    [
+        ("dense", (100, 100)),
+        ("csc", (SIZE, 10)),
+        ("csr", (10, SIZE)),
+        ("csc", None),
+        ("csr", None),
+    ],
 )
 def test_read_lazy_h5_chunk_kwargs(arr_type, chunks, tmp_path):
     import dask.distributed as dd
@@ -282,7 +296,11 @@ def test_read_lazy_h5_chunk_kwargs(arr_type, chunks, tmp_path):
     else:
         arr_store = create_sparse_store(arr_type, store)
         X_dask_from_disk = read_elem_as_dask(arr_store["X"], chunks=chunks)
-    assert X_dask_from_disk.chunksize == chunks
+    if chunks is not None:
+        assert X_dask_from_disk.chunksize == chunks
+    else:
+        # assert that sparse chunks are set correctly by default
+        assert X_dask_from_disk.chunksize[bool(arr_type == "csr")] == SIZE
     X_from_disk = read_elem(arr_store["X"])
     file.close()
     with (