issue_comments

Why is chunk getting called here? Does it actually get called every time we load a dataset with chunks? If so, we will need a more sophisticated solution.

This happens specifically on this line: https://github.com/pydata/xarray/blob/ddc352faa6de91f266a1749773d08ae8d6f09683/xarray/core/dataset.py#L438

So perhaps it would make sense to copy encoding specifically in this case, e.g., python new_var = var.chunk(chunks, name=name2, lock=lock) new_var.encoding = var.encoding

Hmm. I would also be happy with explicitly deleting chunks from encoding for now. It's not adding a lot of technical debt.

In the long term, the whole handling of encoding should be revisited, e.g., see https://github.com/pydata/xarray/issues/5082

FWIW, I would also favor dropping encoding['chunks'] after indexing, coarsening, interpolating, etc. Basically anything that changes the array shape or chunk structure.

We already drop all of encoding after indexing. My guess is that we do the same for coarsening and interpolations as well (though I haven't checked).

Xarray knows to drop the dtype encoding after an arithmetic operation. How does that work? To me .chunk feel like a similar case: an operation that invalidates any existing encoding.

To be honest, the existing convention is quite adhoc, just based on what seemed most appropriate at the time.

https://github.com/pydata/xarray/issues/1614 is most comprehensive description of the current state of things.

We were considering saying that attrs and encoding should always use the same rules, but perhaps we should be more aggressive about dropping encoding.

I'm a little conflicted about dealing with encoding['chunks'] specifically in chunk():

• On one hand, it feels inconsistent for this only this single method in xarray to modify part of encoding. Nothing else in xarray (after CF decoding) does this. Effectively encoding['chunks'] is now becoming a part of xarray's data model.
• On the other hand, this would absolutely fix a recurrent pain-point for users, and in that sense it's worth doing.

Maybe this isn't such a big deal in this particular case, especially if we don't think we would need to add such encoding specific logic to any other methods. But are we really sure about that -- what about cases like indexing?

I guess the other alternative to make chunk() and various other methods that would change chunking drop encoding entirely. I don't know if this would really be a better comprehensive solution (I know dropping attrs is much hated), but at least it's an easier mental model.