issue_comments: 1098229361

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https://github.com/pydata/xarray/pull/6475#issuecomment-1098229361 https://api.github.com/repos/pydata/xarray/issues/6475 1098229361 IC_kwDOAMm_X85BdaZx 1217238 2022-04-13T16:04:23Z 2022-04-13T16:04:23Z MEMBER
  • The v3 spec requires a path be specified when calling open_group or open_consolidated. This PR currently just sets a default group name of 'xarray' if one is not specified via the group kwarg to ZarrStore.open_group. I think that is convenient, but one could instead be stricter and raise an error in this case.

Does Zarr v3 have a notion of a "root" group? That feels like a more sensible default to me, both for Xarray and Zarr-Python

  • If a string corresponding to a filesystem path or URL is used for store, then it is not possible to infer which version of the zarr spec is desired. In this case, the user must specify zarr_version to choose the zarr protocol version. The default of zarr_version=None will infer the version from a zarr BaseStore subclass when possible, otherwise defaulting to zarr_version=2 for backwards compatibility.

This sounds fine for now, but I am concerned that it will slow the adoption of Zarr v3. Eventually, we would presumably want to change the default to version 3, but this is difficult to do if it entirely breaks backwards compatibility.

My preference would be for the default behavior to try opening Zarr v2, and fall back to opening in v3 mode, even if this requires attempting to open a file from the store. This is similar to how Xarray handles other Zarr versioning issues (e.g., for consolidated metadata). Perhaps Zarr-Python could raise an informative error that we could catch if the Zarr version is incorrect, or even handle this behavior itself?

 
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