issue_comments: 1254873700

I have managed to reduce the reproducing example (see "Minimal Complete Verifiable Example 2" above) and then also find a proper solution to fix this issue. I am still not sure whether this is a bug or intended behavior, so I'll won't close the issue for now.

Basically the issue occurs when a chunked NetCDF file is loaded from disk, passed to xarray.map_blocks() and is then used in .sel() as parameter to get a subset of some other xarray object which is not passed to the worker func(). I think the proper solution is to use the args parameter of map_blocks() instead of .sel():

``` --- run-broken.py 2022-09-22 13:00:41.095555961 +0200 +++ run.py 2022-09-22 13:01:14.452696511 +0200 @@ -30,17 +30,17 @@ def resample_annually(data): return data.sortby("time").resample(time="1A", label="left", loffset="1D").mean(dim="time")

• def worker(data):
• locations_chunk = locations.sel(locations=data.locations)
• out_raw = data * locations_chunk
• def worker(data, locations):

• out_raw = data * locations out = resample_annually(out_raw) return out

  template = resample_annually(data)

  out = xr.map_blocks( - lambda data: worker(data).compute().chunk({"time": None}), + lambda data, locations: worker(data, locations).compute().chunk({"time": None}), data, + (locations,), template=template, ) ```

This seems to fix this issue and seems to be the proper solution anyway.

I still don't see why I am not allowed to use .sel() on shadowed objects in the worker func()´. Is this on purpose? If yes, should we add something to the documentation? Is this a specific behavior ofmap_blocks()`? Is it related to #6904?