dask-ms 0.3.0-alpha.1: call for testing and breaking changes

[sjperkins]

dask-ms 0.3.0-alpha.1 is on PyPI. It replaces python-casacore with arcae in the CASA backend, and moves the experimental zarr backend to zarr-python 3. We'd like downstream projects to test it before 0.3.0 final, which pip will install automatically for any project that doesn't cap dask-ms<0.3.

Try it

pip install --pre "dask-ms==0.3.0a1"

pip and uv skip pre-releases unless asked. The alpha won't reach your users until you opt in.

Why

python-casacore is neither thread-safe nor able to release the GIL. dask-ms used to work around this by running all I/O for a table on one thread. arcae releases the GIL and reads through several independent table instances, so CASA reads and writes now run in parallel across dask threads.

Breaking changes

• python-casacore is no longer a dependency. If your code imports casacore (or pyrap) and relied on dask-ms to install it, add python-casacore to your own dependencies. arcae statically links its own casacore, so it can be imported alongside python-casacore.
• daskms.TableProxy is gone, replaced by daskms.CasaTable. table_proxy=True now returns a CasaTable wrapping an arcae Table, not a python-casacore-like proxy. Code that called getcol/putcol/submit on the returned proxy needs updating.
• Removed modules: daskms.optimisation (cached_array, inlined_array), daskms.table_proxy, daskms.table_executor and daskms.ordering.
• zarr-python 3: the zarr, katdal and complete extras now require zarr>=3.1.3. dask-ms still writes the zarr v2 format, but string columns are now stored as VariableLengthUTF8. Stores with string columns written by dask-ms 0.2.x can't be read and raise an informative error.
• Python 3.11–3.14. Python 3.10 is no longer supported. Python 3.14 is now supported.

Additions

• xds_from_table / xds_from_ms take an optional epoch. Calls with the same table, grouping, indexing, taql_where and epoch share one read of the table's row structure. The default (a fresh random epoch) keeps the old behaviour.

taql_where behaves as before: dask-ms still uses Python-style (0-based) TaQL indexing.

Reporting problems

Reply here for questions. Please open an issue for bugs and regressions, including your dask-ms, arcae and dask versions. The full changelog is in HISTORY.rst.