Complete deprecation of Dataset.dims returning dict

doc/whats-new.rst

@@ -55,6 +55,9 @@ Breaking changes
    zarr                      2.13     2.14
   ===================== =========  =======
 
+- Changed the return type of :py:meth:`Dataset.dims` and :py:meth:`DatasetGroupBy.dims` to a frozen set,
+  completing the deprecation cycle started in :pull:`8500`. (:pull:`8980`)
+  By `Tom Nicholas <https://github.com/TomNicholas>`_.
 
 Bug fixes
 ~~~~~~~~~

xarray/core/dataset.py

@@ -99,7 +99,6 @@
 from xarray.core.utils import (
     Default,
     Frozen,
-    FrozenMappingWarningOnValuesAccess,
     HybridMappingProxy,
     OrderedSet,
     _default,
@@ -766,22 +765,17 @@ def drop_encoding(self) -> Self:
         return self._replace(variables=variables, encoding={})
 
     @property
-    def dims(self) -> Frozen[Hashable, int]:
-        """Mapping from dimension names to lengths.
+    def dims(self) -> frozenset[Hashable]:
+        """Set of dimension names.
 
         Cannot be modified directly, but is updated when adding new variables.
 
-        Note that type of this object differs from `DataArray.dims`.
-        See `Dataset.sizes` and `DataArray.sizes` for consistently named
-        properties. This property will be changed to return a type more consistent with
-        `DataArray.dims` in the future, i.e. a set of dimension names.
-
         See Also
         --------
         Dataset.sizes
         DataArray.dims
         """
-        return FrozenMappingWarningOnValuesAccess(self._dims)
+        return frozenset(self._dims.keys())
 
     @property
     def sizes(self) -> Frozen[Hashable, int]:

xarray/core/groupby.py

@@ -37,7 +37,6 @@
     T_Xarray,
 )
 from xarray.core.utils import (
-    FrozenMappingWarningOnValuesAccess,
     contains_only_chunked_or_numpy,
     either_dict_or_kwargs,
     emit_user_level_warning,
@@ -1775,7 +1774,18 @@ class DatasetGroupByBase(GroupBy["Dataset"], DatasetGroupbyArithmetic):
     _dims: Frozen[Hashable, int] | None
 
     @property
-    def dims(self) -> Frozen[Hashable, int]:
+    def dims(self) -> frozenset[Hashable]:
+        """Set of dimension names.
+
+        Immutable.
+
+        See Also
+        --------
+        DataArray.dims
+        DataArray.sizes
+        Dataset.sizes
+        """
+
         if self._dims is None:
             (grouper,) = self.groupers
             index = _maybe_squeeze_indices(
@@ -1786,7 +1796,7 @@ def dims(self) -> Frozen[Hashable, int]:
             )
             self._dims = self._obj.isel({self._group_dim: index}).dims
 
-        return FrozenMappingWarningOnValuesAccess(self._dims)
+        return frozenset(self._dims.keys())
 
     def map(
         self,

xarray/core/utils.py

@@ -50,14 +50,11 @@
     Collection,
     Container,
     Hashable,
-    ItemsView,
     Iterable,
     Iterator,
-    KeysView,
     Mapping,
     MutableMapping,
     MutableSet,
-    ValuesView,
 )
 from enum import Enum
 from pathlib import Path
@@ -443,55 +440,6 @@ def FrozenDict(*args, **kwargs) -> Frozen:
     return Frozen(dict(*args, **kwargs))
 
 
-class FrozenMappingWarningOnValuesAccess(Frozen[K, V]):
-    """
-    Class which behaves like a Mapping but warns if the values are accessed.
-
-    Temporary object to aid in deprecation cycle of `Dataset.dims` (see GH issue #8496).
-    `Dataset.dims` is being changed from returning a mapping of dimension names to lengths to just
-    returning a frozen set of dimension names (to increase consistency with `DataArray.dims`).
-    This class retains backwards compatibility but raises a warning only if the return value
-    of ds.dims is used like a dictionary (i.e. it doesn't raise a warning if used in a way that
-    would also be valid for a FrozenSet, e.g. iteration).
-    """
-
-    __slots__ = ("mapping",)
-
-    def _warn(self) -> None:
-        emit_user_level_warning(
-            "The return type of `Dataset.dims` will be changed to return a set of dimension names in future, "
-            "in order to be more consistent with `DataArray.dims`. To access a mapping from dimension names to lengths, "
-            "please use `Dataset.sizes`.",
-            FutureWarning,
-        )
-
-    def __getitem__(self, key: K) -> V:
-        self._warn()
-        return super().__getitem__(key)
-
-    @overload
-    def get(self, key: K, /) -> V | None: ...
-
-    @overload
-    def get(self, key: K, /, default: V | T) -> V | T: ...
-
-    def get(self, key: K, default: T | None = None) -> V | T | None:
-        self._warn()
-        return super().get(key, default)
-
-    def keys(self) -> KeysView[K]:
-        self._warn()
-        return super().keys()
-
-    def items(self) -> ItemsView[K, V]:
-        self._warn()
-        return super().items()
-
-    def values(self) -> ValuesView[V]:
-        self._warn()
-        return super().values()
-
-
 class HybridMappingProxy(Mapping[K, V]):
     """Implements the Mapping interface. Uses the wrapped mapping for item lookup
     and a separate wrapped keys collection for iteration.