`Dataset.to_zarr` compute=False should allow access to awaitable

What happened?

I have xarray, zarr installed, but not dask, and am trying to call to_zarr in an async routine. I am looking for something I can await. The doc claims that a Dask.Delayed is returned. I understand that if I have a dask client open with asynchronous=True I can await the result.

However, not using Dask. Is there some way to get an awaitable from this object without a dask client?

What did you expect to happen?

I should get something back I can await in my async routine.

Minimal Complete Verifiable Example

import xarray as xr
from asyncio import get_event_loop

ds = xr.Dataset(data_vars = dict(x = ('x', [1, 2])))
deld = ds.to_zarr("bar.zarr", compute=False)
loop.run_until_complete(deld. ...?)

Relevant log output

No response

Anything else we need to know?

No response

Environment

INSTALLED VERSIONS

commit: None python: 3.8.5 (default, Sep 4 2020, 02:22:02) [Clang 10.0.0 ] python-bits: 64 OS: Darwin OS-release: 20.6.0 machine: x86_64 processor: i386 byteorder: little LC_ALL: None LANG: en_US.UTF-8 LOCALE: (‘en_US’, ‘UTF-8’) libhdf5: 1.10.4 libnetcdf: 4.7.3

xarray: 2022.3.0 pandas: 1.4.1 numpy: 1.22.3 scipy: 1.6.2 netCDF4: 1.5.3 pydap: None h5netcdf: None h5py: None Nio: None zarr: 2.11.1 cftime: 1.5.1.1 nc_time_axis: None PseudoNetCDF: None rasterio: None cfgrib: None iris: None bottleneck: 1.3.2 dask: 2021.10.0 distributed: 2021.10.0 matplotlib: 3.1.3 cartopy: None seaborn: None numbagg: None fsspec: 2022.02.0 cupy: None pint: None sparse: None setuptools: 60.7.1 pip: 22.0.3 conda: 4.11.0 pytest: 7.1.1 IPython: 7.31.1 sphinx: None

[shaunc]

You can return a awaitable explicitly without declaring async. I’m not sure what the best style is – if there is no await then asyncio will issue a warning in debug mode. Perhaps you can mark it … Alternately, you could pass in an event loop to computed=, which would trigger the task being added with create_task() (as well as being returned?)

As for a contribution … I’m already hacking on something but it isn’t pretty. Will need to think more about how to do it the right way.

[max-sixty]

That makes sense for the fsspec part, but IIUC we’d also have to make the rest of to_zarr async too?

If it could be made to work without a backward-incompatible change , I think we’d be open to the contribution though.