ENH: Enabling Series.round to work with object dtype

doc/source/whatsnew/v3.0.0.rst

@@ -267,6 +267,7 @@ Other enhancements
 - Added :meth:`DataFrame.from_arrow` and :meth:`Series.from_arrow` to import any Arrow-compatible
   data object into a pandas object through the
   `Arrow PyCapsule Protocol <https://arrow.apache.org/docs/format/CDataInterface/PyCapsuleInterface.html>`__ (:issue:`59631`)
+- :meth:`Series.round` now supports object dtypes when the underlying Python objects implement ``__round__`` (:issue:`63444`)
 
 .. ---------------------------------------------------------------------------
 .. _whatsnew_300.notable_bug_fixes:

pandas/core/series.py

@@ -2577,9 +2577,18 @@ def round(self, decimals: int = 0, *args, **kwargs) -> Series:
         4    3.0
         dtype: float64
         """
+
         nv.validate_round(args, kwargs)
-        if self.dtype == "object":
-            raise TypeError("Expected numeric dtype, got object instead.")
+
+        if len(self) == 0:
+            return self.copy()
+
+        if is_object_dtype(self.dtype):
+            values = self._values
+            result = lib.map_infer(values, lambda x: round(x, decimals), convert=False)
+            return self._constructor(result, index=self.index, copy=False).__finalize__(
+                self, method="round"
+            )
         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

@@ -73,9 +73,47 @@ def test_round_ea_boolean(self):
         result.iloc[0] = False
         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."
-        with pytest.raises(TypeError, match=msg):
-            ser.round()
+    @pytest.mark.parametrize(
+        "data,decimals,expected_data",
+        [
+            ([0.2], 0, [0.0]),
+            ([1.234, 2.567], 1, [1.2, 2.6]),
+            ([1.234, 2.567], 2, [1.23, 2.57]),
+            ([1.234, 2.567], 0, [1.0, 3.0]),
+        ],
+    )
+    def test_round_dtype_object(self, data, decimals, expected_data):
+        # GH#63444
+        ser = Series(data, dtype="object")
+        result = ser.round(decimals)
+        expected = Series(expected_data, dtype="object")
+        tm.assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize(
+        "dtype",
+        [
+            None,
+            "float64",
+            "int64",
+            "object",
+        ],
+    )
+    def test_round_empty_series(self, dtype):
+        # GH#63444
+        result = Series(dtype=dtype).round(4)
+        expected = Series(dtype=dtype)
+        tm.assert_series_equal(result, expected)
+
+    @pytest.mark.parametrize(
+        "dtype,data",
+        [
+            ("string", ["a", "b", "c"]),
+            ("category", ["cat1", "cat2", "cat3"]),
+            (pd.StringDtype(), ["x", "y", "z"]),
+        ],
+    )
+    def test_round_non_numeric_dtype_noop(self, dtype, data):
+        # GH#63444, GH#63559
+        ser = Series(data, dtype=dtype)
+        result = ser.round(2)
+        tm.assert_series_equal(result, ser)