Should str.format() work on xarray scalars?

[fmaussion]

Consider:

da = xr.DataArray([1, 2, 3])
print(f'{da[0]}')
print(f'{da[0]:d}')

Which outputs:

<xarray.DataArray ()>
array(1)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-36-9cd7dc76455b> in <module>
      1 da = xr.DataArray([1, 2, 3])
      2 print(f'{da[0]}')
----> 3 print(f'{da[0]:d}')

TypeError: unsupported format string passed to DataArray.__format__

And the numpy equivalent:

da = xr.DataArray([1, 2, 3]).data
print(f'{da[0]}')
print(f'{da[0]:d}')
1
1

I always found the xarray scalar output to be a bit unfriendly for beginners. In my classes very often scalars are the last output of a computation, and the fact that we can't format the relatively verbose xarray output without resulting to the .data trick is a bit confusing for students (but I agree this is a detail).

Is there a way to get print(f'{da[0]:d}') to work? Thoughts?

[max-sixty]

Allowing __format__ to work could be a nice way of letting us having easy ways to represent scalars, while retaining the benefits of always returning an array from xarray methods.

Separate point but FWIW I generally use .item() to get the value out of a scalar array.

[max-sixty]

@fmaussion how would you envision this working for non-scalar arrays? Would it just raise?

[fmaussion]

@fmaussion how would you envision this working for non-scalar arrays? Would it just raise?

Yes, similar to numpy:

da = xr.DataArray([1, 2, 3]).data
print(f'{da}')
print(f'{da:d}')
[1 2 3]
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-93-e6dbd8f1cf00> in <module>
      1 da = xr.DataArray([1, 2, 3]).data
      2 print(f'{da}')
----> 3 print(f'{da:d}')

TypeError: unsupported format string passed to numpy.ndarray.__format__