`SpatialData.write()` fails for `spatialdata.datasets.blobs()` with `ome-zarr==0.14.0` (`TypeError: Expected an iterable of integers`)

[ArneDefauw]

Summary

After rebuilding a fresh environment SpatialData.write() started failing.

The same code works in an older environment with the same spatialdata, dask, and zarr versions, but with ome-zarr==0.13.0 instead of 0.14.0.

This looks like a regression at the spatialdata / ome-zarr boundary when chunks are passed from xarray/dask to the writer.

Minimal reproducer

import os
import tempfile

from spatialdata.datasets import blobs

sdata = blobs()
out = os.path.join(tempfile.gettempdir(), "sd_blobs_write_issue.zarr")
sdata.write(out)

Observed behavior

The call to sdata.write(out) raises:

TypeError: Expected an iterable of integers. Got ((3,), (512,), (512,)) instead.

Full traceback

Traceback (most recent call last):
 File "<stdin>", line 9, in <module>
 File ".../site-packages/spatialdata/_utils.py", line 263, in wrapper
 return f(*args, **kwargs)
 File ".../site-packages/spatialdata/_core/spatialdata.py", line 1176, in write
 self._write_element(
 File ".../site-packages/spatialdata/_core/spatialdata.py", line 1229, in _write_element
 write_image(
 File ".../site-packages/spatialdata/_io/io_raster.py", line 371, in write_image
 _write_raster(
 File ".../site-packages/spatialdata/_io/io_raster.py", line 197, in _write_raster
 _write_raster_dataarray(
 File ".../site-packages/spatialdata/_io/io_raster.py", line 275, in _write_raster_dataarray
 write_single_scale_ngff(
 File ".../site-packages/ome_zarr/writer.py", line 651, in write_image
 dask_delayed_jobs = _write_pyramid_to_zarr(
 File ".../site-packages/ome_zarr/writer.py", line 754, in _write_pyramid_to_zarr
 da.to_zarr(
 File ".../site-packages/dask/array/core.py", line 4101, in to_zarr
 z = root.create_array(name=array_name, **zarr_array_kwargs)
 File ".../site-packages/zarr/core/group.py", line 2715, in create_array
 self._sync(
 File ".../site-packages/zarr/core/array.py", line 777, in _create_metadata_v3
 chunk_grid_parsed = RegularChunkGrid(chunk_shape=chunk_shape)
 File ".../site-packages/zarr/core/chunk_grids.py", line 180, in __init__
 chunk_shape_parsed = parse_shapelike(chunk_shape)
 File ".../site-packages/zarr/core/common.py", line 200, in parse_shapelike
 raise TypeError(msg)
TypeError: Expected an iterable of integers. Got ((3,), (512,), (512,)) instead.

Version comparison

Failing environment:

Python 3.12.12
spatialdata 0.7.2
ome-zarr 0.14.0
zarr 3.1.5
dask 2026.1.1

Working environment:

Python 3.12.12
spatialdata 0.7.2
ome-zarr 0.13.0
zarr 3.1.5
dask 2026.1.1

So the only relevant version difference I found between the two environments is ome-zarr.

Suspected cause

It looks like spatialdata passes xarray/dask chunk metadata in the form returned by .chunks, i.e. a tuple of tuples:

((3,), (512,), (512,))

In spatialdata/_io/io_raster.py, raster_data.chunks is forwarded into storage_options["chunks"]:

chunks = raster_data.chunks
...
storage_options = {"chunks": chunks}

Then in ome_zarr/writer.py, that value is forwarded into zarr_array_kwargs["chunks"]:

chunks_opt = options.pop("chunks", None)
...
zarr_array_kwargs["chunks"] = chunks_opt

But zarr expects a flat chunk shape like:

(3, 512, 512)

not the dask chunk grid:

((3,), (512,), (512,))

Expected behavior

blobs().write(path) should succeed, or the chunk metadata should be normalized before being passed to Zarr.

Workaround

Pinning ome-zarr==0.13.0 avoids the problem in my setup.

[quentinblampey]

I'm experiencing the same issue!

[LucaMarconato]

Thanks for reporting and for the details. I have investigated this: the bug has been introduced with this PR https://github.com/ome/ome-zarr-py/pull/516/changes#diff-d51ad4cb28d657d5e09c58f40674b95273611983353ab5d7bb2049bbc6303f7b
which adds the line of code that you also referenced:

zarr_array_kwargs["chunks"] = chunks_opt

https://github.com/ome/ome-zarr-py/blob/dcaf13495ba4f85e069cfb71362d1eb30aadaef8/ome_zarr/writer.py#L740

Before that PR, chunks was used only to call .rechunk() https://github.com/ome/ome-zarr-py/blob/585daee36928c7032c8ae8fdb69ad1bb7cef9229/ome_zarr/writer.py#L706, and not passed all the way down to zarr, which triggers the exception.

Flattening the tuple before calling the ome-zarr-py APIs should fix the problem, as suggested above. I will check your PR #1092 @ArneDefauw. I'll also report to ome-zarr-py so that they are made aware of the issue (but fixing downstream as I'll do will be enough to fix this). ome/ome-zarr-py#560