issue_comments

I'm starting to suspect not because that would involve data_array being both DataArray and a Torch.Tensor object. It seems what I'm in fact enabling is that DataArray.data is a Torch.Tensor.

some_sum is still a DataArray, which doesn't have a backward method. You could use data_array = xr.DataArray( xr_tsr, coords=dict(a=["a1", "a2", "a3"], b=["b1", "b1"]), dims=["a", "b"], name="dummy", attrs={"grad": xr_tsr.grad, "backward": xr_tsr.backward}, ) and your example should work (I assume you meant .grad not .grid).

Does this mean I shouldn't fill out __array_function__ in my subclass? Or is this just a forward looking expectation?

No, adding it should be perfectly fine. The dispatch mechanism itself isn't going anywhere, it's part of numpy and it works. Whether or not torch.Tensor itself has an __array_function__ method isn't too relevant for your subclass.

Note that your the main work in adding __array_function__ is not the dispatch mechanism, but mapping to 100% compatible APIs. That job should have gotten a lot easier now compared to 9 months ago. PyTorch now has a completely matching fft module, and a ~70% complete linalg module in master. And functions in the main namespace have gained dtype keywords, integer-to-float promotion, and other NumPy compat changes. So it should be feasible to write your custom subclass.

Create a custom subclass of PyTorch's Tensors which meets the duck array required methods and attributes. Since this isn't officially supported, looks like I could run into issues getting this subclass to persist through tensor operations.

If you use PyTorch 1.7.1 or later, then Tensor subclasses are much better preserved through pytorch functions and operations like slicing. So a custom subclass, adding the attributes and methods Xarray requires for a duck array should be feasible.

data = as_compatible_data(data)

Looks like you need to patch that internally just a bit, probably adding pytorch to NON_NUMPY_SUPPORTED_ARRAY_TYPES.

Note that I do not expect anymore that we'll be adding __array_function__ to torch.Tensor, and certainly not any time soon. My current expectation is that the "get the correct namespace from an array/tensor object directly" from https://numpy.org/neps/nep-0037-array-module.html#how-to-use-get-array-module and https://data-apis.github.io/array-api/latest/ will turn out to be a much better design long-term.

This is a definite downside of reusing NumPy's existing namespace.

We didn't discuss an alternative very explicitly I think, but at least we'll have wide adoption fast. Hopefully the pain is limited ....

Personally, I think the most viable way to achieve seamless integration with deep learning libraries would be to support integration with JAX, which already implements NumPy's API almost exactly.

Less familiar with that, but pytorch does have experimental XLA support, so that's a start.

I think there has been some discussion about this, but I don't know the current status (CC @rgommers).

The PyTorch team is definitely receptive to the idea of adding __array_function__ and __array_ufunc__, as well as expanding the API for better NumPy compatibility.

Also, they want a Tensor.__torch_function__ styled after __array_function__ so they can make their own API overridable.

The tracking issue for all of this is https://github.com/pytorch/pytorch/issues/22402

The biggest challenge for pytorch would be defining the translation layer that implements NumPy's API.

Agreed. No one is working on __array_function__ at the moment. Implementing it has some backwards compat concerns as well, because people may be relying on np.somefunc(some_torch_tensor) to be coerced to ndarray. It's not a small project, but implementing a prototype with a few function in the torch namespace that are not exactly matching the NumPy API would be a useful way to start pushing this forward.