BUG: Fix display with nested NumPy arrays

[basnijholt]

Currently, the following will fail to display:

importxarrayasxrimportnumpyasnpx=np.empty((2, 2), dtype=object)
foriinrange(2):
forjinrange(2):
x[i, j] =np.zeros(2) # Set to 1D array of size 2ds=xr.DataArray(x)
ds

Click to see the error message

---------------------------------------------------------------------------ValueErrorTraceback (mostrecentcalllast)
File~/Work/pipefunc/.venv/lib/python3.13/site-packages/IPython/core/formatters.py:347, inBaseFormatter.__call__(self, obj)
345method=get_real_method(obj, self.print_method)
346ifmethodisnotNone:
-->347returnmethod()
348returnNone349else:
File~/Work/pipefunc/.venv/lib/python3.13/site-packages/xarray/core/common.py:188, inAbstractArray._repr_html_(self)
186ifOPTIONS["display_style"] =="text":
187returnf"<pre>{escape(repr(self))}</pre>"-->188returnformatting_html.array_repr(self)
File~/Work/pipefunc/.venv/lib/python3.13/site-packages/xarray/core/formatting_html.py:323, inarray_repr(arr)
315arr_name=f"'{arr.name}'"ifgetattr(arr, "name", None) else""317header_components= [
318f"<div class='xr-obj-type'>{obj_type}</div>",
319f"<div class='xr-array-name'>{arr_name}</div>",
320format_dims(dims, indexed_dims),
321 ]
-->323sections= [array_section(arr)]
325ifhasattr(arr, "coords"):
326sections.append(coord_section(arr.coords))
File~/Work/pipefunc/.venv/lib/python3.13/site-packages/xarray/core/formatting_html.py:232, inarray_section(obj)
226collapsed= (
227"checked"228if_get_boolean_with_default("display_expand_data", default=True)
229else""230 )
231variable=getattr(obj, "variable", obj)
-->232preview=escape(inline_variable_array_repr(variable, max_width=70))
233data_repr=short_data_repr_html(obj)
234data_icon=_icon("icon-database")
File~/Work/pipefunc/.venv/lib/python3.13/site-packages/xarray/core/formatting.py:304, ininline_variable_array_repr(var, max_width)
302returnvar._data._repr_inline_(max_width)
303ifgetattr(var, "_in_memory", False):
-->304returnformat_array_flat(var, max_width)
305dask_array_type=array_type("dask")
306ifisinstance(var._data, dask_array_type):
File~/Work/pipefunc/.venv/lib/python3.13/site-packages/xarray/core/formatting.py:223, informat_array_flat(array, max_width)
220# every item will take up at least two characters, but we always want to221# print at least first and last items222max_possibly_relevant=min(max(array.size, 1), max(math.ceil(max_width/2.0), 2))
-->223relevant_front_items=format_items(
224first_n_items(array, (max_possibly_relevant+1) //2)
225 )
226relevant_back_items=format_items(last_n_items(array, max_possibly_relevant//2))
227# interleave relevant front and back items:228# [a, b, c] and [y, z] -> [a, z, b, y, c]File~/Work/pipefunc/.venv/lib/python3.13/site-packages/xarray/core/formatting.py:212, informat_items(x)
209elifnp.logical_not(time_needed).all():
210timedelta_format="date"-->212formatted= [format_item(xi, timedelta_format) forxiinx]
213returnformattedFile~/Work/pipefunc/.venv/lib/python3.13/site-packages/xarray/core/formatting.py:193, informat_item(x, timedelta_format, quote_strings)
191returnrepr(x) ifquote_stringselsex192elifhasattr(x, "dtype") andnp.issubdtype(x.dtype, np.floating):
-->193returnf"{x.item():.4}"194else:
195returnstr(x)
ValueError: canonlyconvertanarrayofsize1toaPythonscalar

Whenever there are size==1 arrays, it currently does work:

importxarrayasxrimportnumpyasnpx=np.empty((2, 2), dtype=object)
foriinrange(2):
forjinrange(2):
x[i, j] =np.zeros((1, 1, 1)) # Set to 3D array of size 1ds=xr.DataArray(x)
ds

Should I add these examples as regression tests anywhere, if so, where?

For context, I am running into this issue in https://github.com/pipefunc/pipefunc where one can put the resulting objects into xarray.Datasets.
For example, see the docs here https://pipefunc.readthedocs.io/en/latest/examples/physics-simulation/ (search for xarray.Dataset).

• Closes #xxxx
• Tests added
• User visible changes (including notable bug fixes) are documented in whats-new.rst
• New functions/methods are listed in api.rst

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[basnijholt]

Now test_slice_in_title_single_item_array is failing with:

 - d = [10.009]
? - ^^^
+ d = 10.01
? ^

This test was introduced in #5948 and touches the exact same code that I changed. I think the test that is failing now is wrong and should be updated to d = [10.009] instead.

[dcherian]

OK please update the test in that case. Merging in main should fix the other "array api" failures

[basnijholt]

@dcherian, I updated the tests, all is passing except some (I believe) unrelated failure.

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