Move get_chunks from zarr.py to dataset.py (#4632)

* move get_chunks from zarr to dateset and removed maybe_chunks in zarr

* move get_chunks from zarr to dateset and removed maybe_chunks in zarr

* black

* removed not used import

* update warning message in get_chunks

* Reformat warning text to use f-strings

Co-authored-by: Alessandro Amici <a.amici@bopen.eu>

Author: aurghs

xarray/backends/api.py

@@ -26,7 +26,7 @@
     combine_by_coords,
 )
 from ..core.dataarray import DataArray
-from ..core.dataset import Dataset, _maybe_chunk
+from ..core.dataset import Dataset, _get_chunk, _maybe_chunk
 from ..core.utils import close_on_error, is_grib_path, is_remote_uri
 from .common import AbstractDataStore, ArrayWriter
 from .locks import _get_scheduler
@@ -536,7 +536,7 @@ def maybe_decode_store(store, chunks):
                 k: _maybe_chunk(
                     k,
                     v,
-                    store.get_chunk(k, v, chunks),
+                    _get_chunk(k, v, chunks),
                     overwrite_encoded_chunks=overwrite_encoded_chunks,
                 )
                 for k, v in ds.variables.items()

xarray/backends/apiv2.py

@@ -1,7 +1,8 @@
 import os
 
+from ..core.dataset import _get_chunk, _maybe_chunk
 from ..core.utils import is_remote_uri
-from . import plugins, zarr
+from . import plugins
 from .api import (
     _autodetect_engine,
     _get_backend_cls,
@@ -54,10 +55,15 @@ def dataset_from_backend_dataset(
         if isinstance(chunks, int):
             chunks = dict.fromkeys(ds.dims, chunks)
 
-        variables = {
-            k: zarr.ZarrStore.maybe_chunk(k, v, chunks, overwrite_encoded_chunks)
-            for k, v in ds.variables.items()
-        }
+        variables = {}
+        for k, v in ds.variables.items():
+            var_chunks = _get_chunk(k, v, chunks)
+            variables[k] = _maybe_chunk(
+                k,
+                v,
+                var_chunks,
+                overwrite_encoded_chunks=overwrite_encoded_chunks,
+            )
         ds2 = ds._replace(variables)
 
     else:

xarray/backends/zarr.py

@@ -1,5 +1,3 @@
-import warnings
-
 import numpy as np
 
 from .. import coding, conventions
@@ -368,53 +366,6 @@ def encode_variable(self, variable):
     def encode_attribute(self, a):
         return encode_zarr_attr_value(a)
 
-    @staticmethod
-    def get_chunk(name, var, chunks):
-        chunk_spec = dict(zip(var.dims, var.encoding.get("chunks")))
-
-        # Coordinate labels aren't chunked
-        if var.ndim == 1 and var.dims[0] == name:
-            return chunk_spec
-
-        if chunks == "auto":
-            return chunk_spec
-
-        for dim in var.dims:
-            if dim in chunks:
-                spec = chunks[dim]
-                if isinstance(spec, int):
-                    spec = (spec,)
-                if isinstance(spec, (tuple, list)) and chunk_spec[dim]:
-                    if any(s % chunk_spec[dim] for s in spec):
-                        warnings.warn(
-                            "Specified Dask chunks %r would "
-                            "separate Zarr chunk shape %r for "
-                            "dimension %r. This significantly "
-                            "degrades performance. Consider "
-                            "rechunking after loading instead."
-                            % (chunks[dim], chunk_spec[dim], dim),
-                            stacklevel=2,
-                        )
-                chunk_spec[dim] = chunks[dim]
-        return chunk_spec
-
-    @classmethod
-    def maybe_chunk(cls, name, var, chunks, overwrite_encoded_chunks):
-        chunk_spec = cls.get_chunk(name, var, chunks)
-
-        if (var.ndim > 0) and (chunk_spec is not None):
-            from dask.base import tokenize
-
-            # does this cause any data to be read?
-            token2 = tokenize(name, var._data, chunks)
-            name2 = f"xarray-{name}-{token2}"
-            var = var.chunk(chunk_spec, name=name2, lock=None)
-            if overwrite_encoded_chunks and var.chunks is not None:
-                var.encoding["chunks"] = tuple(x[0] for x in var.chunks)
-            return var
-        else:
-            return var
-
     def store(
         self,
         variables,

xarray/core/dataset.py

@@ -359,6 +359,34 @@ def _assert_empty(args: tuple, msg: str = "%s") -> None:
         raise ValueError(msg % args)
 
 
+def _get_chunk(name, var, chunks):
+    chunk_spec = dict(zip(var.dims, var.encoding.get("chunks")))
+
+    # Coordinate labels aren't chunked
+    if var.ndim == 1 and var.dims[0] == name:
+        return chunk_spec
+
+    if chunks == "auto":
+        return chunk_spec
+
+    for dim in var.dims:
+        if dim in chunks:
+            spec = chunks[dim]
+            if isinstance(spec, int):
+                spec = (spec,)
+            if isinstance(spec, (tuple, list)) and chunk_spec[dim]:
+                if any(s % chunk_spec[dim] for s in spec):
+                    warnings.warn(
+                        f"Specified Dask chunks {chunks[dim]} would separate "
+                        f"on disks chunk shape {chunk_spec[dim]} for dimension {dim}. "
+                        "This could degrade performance. "
+                        "Consider rechunking after loading instead.",
+                        stacklevel=2,
+                    )
+            chunk_spec[dim] = chunks[dim]
+    return chunk_spec
+
+
 def _maybe_chunk(
     name,
     var,