DEPR: drop setting categorical codes

doc/source/whatsnew/v2.0.0.rst

@@ -198,6 +198,7 @@ Removal of prior version deprecations/changes
 - Removed ``pandas.SparseArray`` in favor of :class:`arrays.SparseArray` (:issue:`30642`)
 - Removed ``pandas.SparseSeries`` and ``pandas.SparseDataFrame`` (:issue:`30642`)
 - Enforced disallowing a string column label into ``times`` in :meth:`DataFrame.ewm` (:issue:`43265`)
+- Removed setting Categorical._codes directly (:issue:`41429`)
 - Enforced :meth:`Rolling.count` with ``min_periods=None`` to default to the size of the window (:issue:`31302`)
 -
 

pandas/core/arrays/categorical.py

@@ -2059,16 +2059,6 @@ def _values_for_rank(self):
     def _codes(self) -> np.ndarray:
         return self._ndarray
 
-    @_codes.setter
-    def _codes(self, value: np.ndarray) -> None:
-        warn(
-            "Setting the codes on a Categorical is deprecated and will raise in "
-            "a future version. Create a new Categorical object instead",
-            FutureWarning,
-            stacklevel=find_stack_level(),
-        )  # GH#40606
-        NDArrayBacked.__init__(self, value, self.dtype)
-
     def _box_func(self, i: int):
         if i == -1:
             return np.NaN

pandas/tests/arrays/categorical/test_api.py

@@ -516,15 +516,6 @@ def test_set_categories_inplace(self, factor):
 
         tm.assert_index_equal(cat.categories, Index(["a", "b", "c", "d"]))
 
-    def test_codes_setter_deprecated(self):
-        cat = Categorical([1, 2, 3, 1, 2, 3, 3, 2, 1, 1, 1])
-        new_codes = cat._codes + 1
-        with tm.assert_produces_warning(FutureWarning):
-            # GH#40606
-            cat._codes = new_codes
-
-        assert cat._codes is new_codes
-
 
 class TestPrivateCategoricalAPI:
     def test_codes_immutable(self):