BUG/TST: Series round with dtype object

doc/source/whatsnew/v3.0.0.rst

@@ -210,6 +210,7 @@ Other enhancements
 - :meth:`Series.map` can now accept kwargs to pass on to func (:issue:`59814`)
 - :meth:`Series.map` now accepts an ``engine`` parameter to allow execution with a third-party execution engine (:issue:`61125`)
 - :meth:`Series.rank` and :meth:`DataFrame.rank` with numpy-nullable dtypes preserve ``NA`` values and return ``UInt64`` dtype where appropriate instead of casting ``NA`` to ``NaN`` with ``float64`` dtype (:issue:`62043`)
+- :meth:`Series.round` now operates pointwise on columns of object dtype (:issue:`62174`)
 - :meth:`Series.str.get_dummies` now accepts a  ``dtype`` parameter to specify the dtype of the resulting DataFrame (:issue:`47872`)
 - :meth:`pandas.concat` will raise a ``ValueError`` when ``ignore_index=True`` and ``keys`` is not ``None`` (:issue:`59274`)
 - :py:class:`frozenset` elements in pandas objects are now natively printed (:issue:`60690`)

pandas/core/internals/blocks.py

@@ -1,5 +1,6 @@
 from __future__ import annotations
 
+import functools
 import inspect
 import re
 from typing import (
@@ -1503,16 +1504,28 @@ def quantile(
     def round(self, decimals: int) -> Self:
         """
         Rounds the values.
-        If the block is not of an integer or float dtype, nothing happens.
-        This is consistent with DataFrame.round behavior.
-        (Note: Series.round would raise)
+        If the block is of object dtype, it will operate pointwise and possibly raise.
+        Otherwise, if the block is not of an integer or float dtype, nothing happens.
 
         Parameters
         ----------
         decimals: int,
             Number of decimal places to round to.
             Caller is responsible for validating this
         """
+        if self.dtype == _dtype_obj:
+            round_func = functools.partial(round, ndigits=decimals)
+            try:
+                values = algos.map_array(self.values, round_func)
+            except TypeError as err:
+                raise TypeError("Expected numeric entries for dtype object.") from err
+
+            refs = None
+            if values is self.values:
+                refs = self.refs
+
+            return self.make_block_same_class(values, refs=refs)
+
         if not self.is_numeric or self.is_bool:
             return self.copy(deep=False)
         # TODO: round only defined on BaseMaskedArray

pandas/core/series.py

@@ -2514,8 +2514,6 @@ def round(self, decimals: int = 0, *args, **kwargs) -> Series:
         dtype: float64
         """
         nv.validate_round(args, kwargs)
-        if self.dtype == "object":
-            raise TypeError("Expected numeric dtype, got object instead.")
         new_mgr = self._mgr.round(decimals=decimals)
         return self._constructor_from_mgr(new_mgr, axes=new_mgr.axes).__finalize__(
             self, method="round"

pandas/tests/series/methods/test_round.py

@@ -74,8 +74,11 @@ def test_round_ea_boolean(self):
         tm.assert_series_equal(ser, expected)
 
     def test_round_dtype_object(self):
-        # GH#61206
-        ser = Series([0.2], dtype="object")
-        msg = "Expected numeric dtype, got object instead."
+        # GH#61206, GH#62174
+        ser = Series([0.232], dtype="object")
+        expected = Series([0.2])
+        tm.assert_series_equal(ser.round(1), expected)
+        ser2 = Series(["bar"], dtype="object")
+        msg = "Expected numeric entries for dtype object."
         with pytest.raises(TypeError, match=msg):
-            ser.round()
+            ser2.round()