Xarray attrs (attributes) nested case propagation

[phockett]

Noticed that xr.copy() isn't deep-copying nested dicts (note xr.copy(deep=True) is default, see https://docs.xarray.dev/en/stable/generated/xarray.DataArray.copy.html).

Fixed for sphRealConvert() in e2ad5eb, but may need to propagate elsewhere.

E.g.

    dataCalc = dataIn.copy()   # Works for base attrs dict, but not nested dicts.
    dataCalc.attrs = copy.deepcopy(dataIn.attrs)  # THIS WORKS ALSO FOR NESTED DICT CASE

TODO: may have also fixed elsewhere? See PEMtk and IO codes for more .attrs handling methods.

TODO: check Xarray versions, tested in 2022.3.0 which is not latest.

See also pydata/xarray#2835

UPDATE: this is an issue in 2022.3.0, but not in 2022.6.0.

[phockett]

# MINIMAL EXAMPLE, tested in XR 2022.3.0

import xarray as xr
import numpy as np

data = xr.DataArray(np.random.randn(2, 3), dims=("x", "y"), coords={"x": [10, 20]})
data.attrs['flat']='0'
data.attrs['nested']={'level1':'1'}

data2 = data.copy(deep=True)
data2.attrs['flat']='2'  # OK
# data2.attrs['nested']={'level1':'2'}  # OK
# data2.attrs['nested']['level1'] = '2'  # Fails - overwrites data
data2.attrs['nested'].update({'level1':'2'})  # Fails - overwrites data

print(data.attrs)
print(data2.attrs)

Outputs

{'flat': '0', 'nested': {'level1': '2'}}
{'flat': '2', 'nested': {'level1': '2'}}

Safe attrs copy with:

data2 = data.copy(deep=True)
data2.attrs = copy.deepcopy(data.attrs)

[phockett]

Manual fix applied in new sphConv functions, but may be an issue elsewhere at the moment.

Xarray >2022.6.0 should also have this issue fixed, as of 29/09/22, see pydata/xarray#2835 and pydata/xarray#7089.