Unit handling in xarray fails for Python 3.12

[crdanielbusch]

Describe the bug

The function pr.sum removes the units in a dataset for Python version 3.12.2

Failing Test

github_issue_ds_1.csv

import primap2 as pm

test_data = pm.open_dataset("github_issue_ds_1.csv")

test_data = test_data.pr.sum(dim="category", skipna=True, min_count=1)

print(test_data.pr.to_interchange_format()['unit'])

Output for Python 3.10.13:

0      CH4 * gigagram / a
1       CO * gigagram / a
2      CO2 * gigagram / a
3      N2O * gigagram / a
4    NMVOC * gigagram / a
5      NOx * gigagram / a
6      SO2 * gigagram / a
Name: unit, dtype: object

Output for Python 3.12.2:

/Users/danielbusch/Documents/UNFCCC_non-AnnexI_data/venv/lib/python3.12/site-packages/xarray/namedarray/core.py:215: UnitStrippedWarning: The unit of the quantity is stripped when downcasting to ndarray.
  return NamedArray(dims, np.asarray(data), attrs)
/Users/danielbusch/Documents/UNFCCC_non-AnnexI_data/venv/lib/python3.12/site-packages/xarray/namedarray/core.py:215: UnitStrippedWarning: The unit of the quantity is stripped when downcasting to ndarray.
  return NamedArray(dims, np.asarray(data), attrs)
/Users/danielbusch/Documents/UNFCCC_non-AnnexI_data/venv/lib/python3.12/site-packages/xarray/namedarray/core.py:215: UnitStrippedWarning: The unit of the quantity is stripped when downcasting to ndarray.
  return NamedArray(dims, np.asarray(data), attrs)
/Users/danielbusch/Documents/UNFCCC_non-AnnexI_data/venv/lib/python3.12/site-packages/xarray/namedarray/core.py:215: UnitStrippedWarning: The unit of the quantity is stripped when downcasting to ndarray.
  return NamedArray(dims, np.asarray(data), attrs)
/Users/danielbusch/Documents/UNFCCC_non-AnnexI_data/venv/lib/python3.12/site-packages/xarray/namedarray/core.py:215: UnitStrippedWarning: The unit of the quantity is stripped when downcasting to ndarray.
  return NamedArray(dims, np.asarray(data), attrs)
/Users/danielbusch/Documents/UNFCCC_non-AnnexI_data/venv/lib/python3.12/site-packages/xarray/namedarray/core.py:215: UnitStrippedWarning: The unit of the quantity is stripped when downcasting to ndarray.
  return NamedArray(dims, np.asarray(data), attrs)
/Users/danielbusch/Documents/UNFCCC_non-AnnexI_data/venv/lib/python3.12/site-packages/xarray/namedarray/core.py:215: UnitStrippedWarning: The unit of the quantity is stripped when downcasting to ndarray.
  return NamedArray(dims, np.asarray(data), attrs)
/Users/danielbusch/Documents/UNFCCC_non-AnnexI_data/venv/lib/python3.12/site-packages/xarray/namedarray/core.py:215: UnitStrippedWarning: The unit of the quantity is stripped when downcasting to ndarray.
  return NamedArray(dims, np.asarray(data), attrs)
/Users/danielbusch/Documents/UNFCCC_non-AnnexI_data/venv/lib/python3.12/site-packages/xarray/namedarray/core.py:215: UnitStrippedWarning: The unit of the quantity is stripped when downcasting to ndarray.
  return NamedArray(dims, np.asarray(data), attrs)
/Users/danielbusch/Documents/UNFCCC_non-AnnexI_data/venv/lib/python3.12/site-packages/xarray/namedarray/core.py:215: UnitStrippedWarning: The unit of the quantity is stripped when downcasting to ndarray.
  return NamedArray(dims, np.asarray(data), attrs)
0    no unit
1    no unit
2    no unit
3    no unit
4    no unit
5    no unit
6    no unit
Name: unit, dtype: object

Expected behavior

The sum function should calculate the sum over the given dimension and keep all the unit information.

System (please complete the following information):

• OS: [macOS]
• Python version 3.12.2