Declare Dataset, DataArray, Variable, GroupBy unhashable (#8392)

* Add unhashable to generate_ops

* Regenerate _typed_ops after adding "unhashable"

* Fix variable redefinition

The previous commit revealed the following mypy error:

xarray/core/dataset.py: note: In member "swap_dims" of class "Dataset":
xarray/core/dataset.py:4415: error: Incompatible types in assignment (expression has type "Variable", variable has type "Hashable")  [assignment]
xarray/core/dataset.py:4415: note: Following member(s) of "Variable" have conflicts:
xarray/core/dataset.py:4415: note:     __hash__: expected "Callable[[], int]", got "None"
xarray/core/dataset.py:4416: error: "Hashable" has no attribute "dims"  [attr-defined]
xarray/core/dataset.py:4419: error: "Hashable" has no attribute "to_index_variable"  [attr-defined]
xarray/core/dataset.py:4430: error: "Hashable" has no attribute "to_base_variable"  [attr-defined]

xarray/core/_typed_ops.py

@@ -83,6 +83,10 @@ def __eq__(self, other: DsCompatible) -> Self:  # type:ignore[override]
     def __ne__(self, other: DsCompatible) -> Self:  # type:ignore[override]
         return self._binary_op(other, nputils.array_ne)
 
+    # When __eq__ is defined but __hash__ is not, then an object is unhashable,
+    # and it should be declared as follows:
+    __hash__: None  # type:ignore[assignment]
+
     def __radd__(self, other: DsCompatible) -> Self:
         return self._binary_op(other, operator.add, reflexive=True)
 
@@ -291,6 +295,10 @@ def __eq__(self, other: DaCompatible) -> Self:  # type:ignore[override]
     def __ne__(self, other: DaCompatible) -> Self:  # type:ignore[override]
         return self._binary_op(other, nputils.array_ne)
 
+    # When __eq__ is defined but __hash__ is not, then an object is unhashable,
+    # and it should be declared as follows:
+    __hash__: None  # type:ignore[assignment]
+
     def __radd__(self, other: DaCompatible) -> Self:
         return self._binary_op(other, operator.add, reflexive=True)
 
@@ -643,6 +651,10 @@ def __ne__(self, other: VarCompatible) -> Self:
     def __ne__(self, other: VarCompatible) -> Self | T_DataArray:
         return self._binary_op(other, nputils.array_ne)
 
+    # When __eq__ is defined but __hash__ is not, then an object is unhashable,
+    # and it should be declared as follows:
+    __hash__: None  # type:ignore[assignment]
+
     def __radd__(self, other: VarCompatible) -> Self:
         return self._binary_op(other, operator.add, reflexive=True)
 
@@ -851,6 +863,10 @@ def __eq__(self, other: GroupByCompatible) -> Dataset:  # type:ignore[override]
     def __ne__(self, other: GroupByCompatible) -> Dataset:  # type:ignore[override]
         return self._binary_op(other, nputils.array_ne)
 
+    # When __eq__ is defined but __hash__ is not, then an object is unhashable,
+    # and it should be declared as follows:
+    __hash__: None  # type:ignore[assignment]
+
     def __radd__(self, other: GroupByCompatible) -> Dataset:
         return self._binary_op(other, operator.add, reflexive=True)
 
@@ -973,6 +989,10 @@ def __eq__(self, other: T_Xarray) -> T_Xarray:  # type:ignore[override]
     def __ne__(self, other: T_Xarray) -> T_Xarray:  # type:ignore[override]
         return self._binary_op(other, nputils.array_ne)
 
+    # When __eq__ is defined but __hash__ is not, then an object is unhashable,
+    # and it should be declared as follows:
+    __hash__: None  # type:ignore[assignment]
+
     def __radd__(self, other: T_Xarray) -> T_Xarray:
         return self._binary_op(other, operator.add, reflexive=True)
 

xarray/core/dataset.py

@@ -4410,16 +4410,18 @@ def swap_dims(
         # rename_dims() method that only renames dimensions.
 
         dims_dict = either_dict_or_kwargs(dims_dict, dims_kwargs, "swap_dims")
-        for k, v in dims_dict.items():
-            if k not in self.dims:
+        for current_name, new_name in dims_dict.items():
+            if current_name not in self.dims:
                 raise ValueError(
-                    f"cannot swap from dimension {k!r} because it is "
+                    f"cannot swap from dimension {current_name!r} because it is "
                     f"not one of the dimensions of this dataset {tuple(self.dims)}"
                 )
-            if v in self.variables and self.variables[v].dims != (k,):
+            if new_name in self.variables and self.variables[new_name].dims != (
+                current_name,
+            ):
                 raise ValueError(
-                    f"replacement dimension {v!r} is not a 1D "
-                    f"variable along the old dimension {k!r}"
+                    f"replacement dimension {new_name!r} is not a 1D "
+                    f"variable along the old dimension {current_name!r}"
                 )
 
         result_dims = {dims_dict.get(dim, dim) for dim in self.dims}
@@ -4429,24 +4431,24 @@ def swap_dims(
 
         variables: dict[Hashable, Variable] = {}
         indexes: dict[Hashable, Index] = {}
-        for k, v in self.variables.items():
-            dims = tuple(dims_dict.get(dim, dim) for dim in v.dims)
+        for current_name, current_variable in self.variables.items():
+            dims = tuple(dims_dict.get(dim, dim) for dim in current_variable.dims)
             var: Variable
-            if k in result_dims:
-                var = v.to_index_variable()
+            if current_name in result_dims:
+                var = current_variable.to_index_variable()
                 var.dims = dims
-                if k in self._indexes:
-                    indexes[k] = self._indexes[k]
-                    variables[k] = var
+                if current_name in self._indexes:
+                    indexes[current_name] = self._indexes[current_name]
+                    variables[current_name] = var
                 else:
                     index, index_vars = create_default_index_implicit(var)
                     indexes.update({name: index for name in index_vars})
                     variables.update(index_vars)
                     coord_names.update(index_vars)
             else:
-                var = v.to_base_variable()
+                var = current_variable.to_base_variable()
                 var.dims = dims
-                variables[k] = var
+                variables[current_name] = var
 
         return self._replace_with_new_dims(variables, coord_names, indexes=indexes)
 

xarray/util/generate_ops.py

@@ -116,6 +116,10 @@ def {method}(self) -> Self:
 template_other_unary = """
     def {method}(self, *args: Any, **kwargs: Any) -> Self:
         return self._unary_op({func}, *args, **kwargs)"""
+unhashable = """
+    # When __eq__ is defined but __hash__ is not, then an object is unhashable,
+    # and it should be declared as follows:
+    __hash__: None  # type:ignore[assignment]"""
 
 # For some methods we override return type `bool` defined by base class `object`.
 # We need to add "# type: ignore[override]"
@@ -152,6 +156,7 @@ def binops(
             template_binop,
             extras | {"type_ignore": _type_ignore(type_ignore_eq)},
         ),
+        ([(None, None)], unhashable, extras),
         (BINOPS_REFLEXIVE, template_reflexive, extras),
     ]
 
@@ -185,6 +190,7 @@ def binops_overload(
                 "overload_type_ignore": _type_ignore(type_ignore_eq),
             },
         ),
+        ([(None, None)], unhashable, extras),
         (BINOPS_REFLEXIVE, template_reflexive, extras),
     ]