DEPR: value_counts doing dtype inference on result.index

doc/source/whatsnew/v3.0.0.rst

@@ -199,6 +199,7 @@ Removal of prior version deprecations/changes
 - All arguments in :meth:`Series.to_dict` are now keyword only (:issue:`56493`)
 - Changed the default value of ``observed`` in :meth:`DataFrame.groupby` and :meth:`Series.groupby` to ``True`` (:issue:`51811`)
 - Enforced deprecation disallowing parsing datetimes with mixed time zones unless user passes ``utc=True`` to :func:`to_datetime` (:issue:`57275`)
+- Enforced deprecation in :meth:`Series.value_counts` and :meth:`Index.value_counts` with object dtype performing dtype inference on the ``.index`` of the result (:issue:`56161`)
 - Enforced deprecation of :meth:`.DataFrameGroupBy.get_group` and :meth:`.SeriesGroupBy.get_group` allowing the ``name`` argument to be a non-tuple when grouping by a list of length 1 (:issue:`54155`)
 - Enforced deprecation of :meth:`Series.interpolate` and :meth:`DataFrame.interpolate` for object-dtype (:issue:`57820`)
 - Enforced deprecation of ``axis=None`` acting the same as ``axis=0`` in the DataFrame reductions ``sum``, ``prod``, ``std``, ``var``, and ``sem``, passing ``axis=None`` will now reduce over both axes; this is particularly the case when doing e.g. ``numpy.sum(df)`` (:issue:`21597`)

pandas/core/algorithms.py

@@ -892,26 +892,9 @@ def value_counts_internal(
             if keys.dtype == np.float16:
                 keys = keys.astype(np.float32)
 
-            # For backwards compatibility, we let Index do its normal type
-            #  inference, _except_ for if if infers from object to bool.
-            idx = Index(keys)
-            if idx.dtype == bool and keys.dtype == object:
-                idx = idx.astype(object)
-            elif (
-                idx.dtype != keys.dtype  # noqa: PLR1714  # # pylint: disable=R1714
-                and idx.dtype != "string[pyarrow_numpy]"
-            ):
-                warnings.warn(
-                    # GH#56161
-                    "The behavior of value_counts with object-dtype is deprecated. "
-                    "In a future version, this will *not* perform dtype inference "
-                    "on the resulting index. To retain the old behavior, use "
-                    "`result.index = result.index.infer_objects()`",
-                    FutureWarning,
-                    stacklevel=find_stack_level(),
-                )
-            idx.name = index_name
-
+            # Starting in 3.0, we no longer perform dtype inference on the
+            #  Index object we construct here, xref GH#56161
+            idx = Index(keys, dtype=keys.dtype, name=index_name)
             result = Series(counts, index=idx, name=name, copy=False)
 
     if sort:
@@ -1606,16 +1589,8 @@ def union_with_duplicates(
     """
     from pandas import Series
 
-    with warnings.catch_warnings():
-        # filter warning from object dtype inference; we will end up discarding
-        # the index here, so the deprecation does not affect the end result here.
-        warnings.filterwarnings(
-            "ignore",
-            "The behavior of value_counts with object-dtype is deprecated",
-            category=FutureWarning,
-        )
-        l_count = value_counts_internal(lvals, dropna=False)
-        r_count = value_counts_internal(rvals, dropna=False)
+    l_count = value_counts_internal(lvals, dropna=False)
+    r_count = value_counts_internal(rvals, dropna=False)
     l_count, r_count = l_count.align(r_count, fill_value=0)
     final_count = np.maximum(l_count.values, r_count.values)
     final_count = Series(final_count, index=l_count.index, dtype="int", copy=False)

pandas/core/arrays/interval.py

@@ -13,7 +13,6 @@
     Union,
     overload,
 )
-import warnings
 
 import numpy as np
 
@@ -1217,15 +1216,8 @@ def value_counts(self, dropna: bool = True) -> Series:
         Series.value_counts
         """
         # TODO: implement this is a non-naive way!
-        with warnings.catch_warnings():
-            warnings.filterwarnings(
-                "ignore",
-                "The behavior of value_counts with object-dtype is deprecated",
-                category=FutureWarning,
-            )
-            result = value_counts(np.asarray(self), dropna=dropna)
-            # Once the deprecation is enforced, we will need to do
-            #  `result.index = result.index.astype(self.dtype)`
+        result = value_counts(np.asarray(self), dropna=dropna)
+        result.index = result.index.astype(self.dtype)
         return result
 
     # ---------------------------------------------------------------------

pandas/tests/base/test_value_counts.py

@@ -347,9 +347,8 @@ def test_value_counts_object_inference_deprecated():
     dti = pd.date_range("2016-01-01", periods=3, tz="UTC")
 
     idx = dti.astype(object)
-    msg = "The behavior of value_counts with object-dtype is deprecated"
-    with tm.assert_produces_warning(FutureWarning, match=msg):
-        res = idx.value_counts()
+    res = idx.value_counts()
 
     exp = dti.value_counts()
+    exp.index = exp.index.astype(object)
     tm.assert_series_equal(res, exp)