Iterable[Dataset | DataArray] issue with xarray.core.combine.combine_by_coords

[leaver2000]

What is your issue?

I wanted to highlight a typing issue with xarray.core.combine.combine_by_coords where the first argument is data_objects: Iterable[Dataset | DataArray] = []. Specifically the type issue exists when a Generator which is an Iterable is passed as the data_objects argument. See the example below...

from typing import Iterable
import xarray as xr

def dataset_maker(key:str) -> xr.Dataset:
    return xr.Dataset(
        data_vars={
            key: xr.DataArray(data=[1, 2, 3], dims=["x"])
        },
        coords=dict(
            x=xr.DataArray(data=[1, 2, 3], dims=["x"]),
        ),
    )


data_list = [dataset_maker('a'), dataset_maker('b')]
assert isinstance(data_list, Iterable)
print("... { data_list } ...")
print(xr.combine_by_coords(data_list))

data_tuple = dataset_maker('a'), dataset_maker('b')
assert isinstance(data_tuple, Iterable)
print("... { data_tuple } ...")
print(xr.combine_by_coords(data_tuple))

data_iterator = (dataset_maker(k) for k in ['a', 'b']) 
assert isinstance(data_iterator, Iterable)
print("... { data_iterator } ...")
print(xr.combine_by_coords(data_iterator))

The results.

... { data_list } ...
<xarray.Dataset> Size: 72B
Dimensions:  (x: 3)
Coordinates:
  * x        (x) int64 24B 1 2 3
Data variables:
    a        (x) int64 24B 1 2 3
    b        (x) int64 24B 1 2 3
... { data_tuple } ...
<xarray.Dataset> Size: 72B
Dimensions:  (x: 3)
Coordinates:
  * x        (x) int64 24B 1 2 3
Data variables:
    a        (x) int64 24B 1 2 3
    b        (x) int64 24B 1 2 3
... { data_iterator } ...
<xarray.Dataset> Size: 0B
Dimensions:  ()
Data variables:
    *empty*

The issue arises at the head of the function where the generator is exhausted.

    objs_are_unnamed_dataarrays = [
        isinstance(data_object, DataArray) and data_object.name is None
        for data_object in data_objects
    ]

A simple solution would be to change the type annotations to either that of a Sequence or memoize the data_objects variable as...

data_objects = list(data_objects)

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[max-sixty]

That makes sense — thanks for the issue.

I think materializing it as a list would make sense. Or if it's possible to move the check closer to the code that's operating and avoiding the additional loop, that would work too.

Any chance you'd like to put a small PR in?

[leaver2000]

Any chance you'd like to put a small PR in?

Sure, I'll try and get something submitted tomorrow.