API/REGR: (re-)allow neg/pos unary operation on object dtype (#21590)

Author: jorisvandenbossche

Diff for: doc/source/whatsnew/v0.23.2.txt

@@ -54,6 +54,7 @@ Fixed Regressions
 
 - Fixed regression in :meth:`to_csv` when handling file-like object incorrectly (:issue:`21471`)
 - Bug in both :meth:`DataFrame.first_valid_index` and :meth:`Series.first_valid_index` raised for a row index having duplicate values (:issue:`21441`)
+- Fixed regression in unary negative operations with object dtype (:issue:`21380`)
 - Bug in :meth:`Timestamp.ceil` and :meth:`Timestamp.floor` when timestamp is a multiple of the rounding frequency (:issue:`21262`)
 
 .. _whatsnew_0232.performance:

Diff for: pandas/core/generic.py

@@ -27,6 +27,7 @@
     is_dict_like,
     is_re_compilable,
     is_period_arraylike,
+    is_object_dtype,
     pandas_dtype)
 from pandas.core.dtypes.cast import maybe_promote, maybe_upcast_putmask
 from pandas.core.dtypes.inference import is_hashable
@@ -1117,7 +1118,8 @@ def __neg__(self):
         values = com._values_from_object(self)
         if is_bool_dtype(values):
             arr = operator.inv(values)
-        elif (is_numeric_dtype(values) or is_timedelta64_dtype(values)):
+        elif (is_numeric_dtype(values) or is_timedelta64_dtype(values)
+                or is_object_dtype(values)):
             arr = operator.neg(values)
         else:
             raise TypeError("Unary negative expects numeric dtype, not {}"
@@ -1128,7 +1130,8 @@ def __pos__(self):
         values = com._values_from_object(self)
         if (is_bool_dtype(values) or is_period_arraylike(values)):
             arr = values
-        elif (is_numeric_dtype(values) or is_timedelta64_dtype(values)):
+        elif (is_numeric_dtype(values) or is_timedelta64_dtype(values)
+                or is_object_dtype(values)):
             arr = operator.pos(values)
         else:
             raise TypeError("Unary plus expects numeric dtype, not {}"

Diff for: pandas/tests/frame/test_operators.py

@@ -3,6 +3,7 @@
 from __future__ import print_function
 from collections import deque
 from datetime import datetime
+from decimal import Decimal
 import operator
 
 import pytest
@@ -282,6 +283,17 @@ def test_neg_numeric(self, df, expected):
         assert_frame_equal(-df, expected)
         assert_series_equal(-df['a'], expected['a'])
 
+    @pytest.mark.parametrize('df, expected', [
+        (np.array([1, 2], dtype=object), np.array([-1, -2], dtype=object)),
+        ([Decimal('1.0'), Decimal('2.0')], [Decimal('-1.0'), Decimal('-2.0')]),
+    ])
+    def test_neg_object(self, df, expected):
+        # GH 21380
+        df = pd.DataFrame({'a': df})
+        expected = pd.DataFrame({'a': expected})
+        assert_frame_equal(-df, expected)
+        assert_series_equal(-df['a'], expected['a'])
+
     @pytest.mark.parametrize('df', [
         pd.DataFrame({'a': ['a', 'b']}),
         pd.DataFrame({'a': pd.to_datetime(['2017-01-22', '1970-01-01'])}),
@@ -307,6 +319,15 @@ def test_pos_numeric(self, df):
 
     @pytest.mark.parametrize('df', [
         pd.DataFrame({'a': ['a', 'b']}),
+        pd.DataFrame({'a': np.array([-1, 2], dtype=object)}),
+        pd.DataFrame({'a': [Decimal('-1.0'), Decimal('2.0')]}),
+    ])
+    def test_pos_object(self, df):
+        # GH 21380
+        assert_frame_equal(+df, df)
+        assert_series_equal(+df['a'], df['a'])
+
+    @pytest.mark.parametrize('df', [
         pd.DataFrame({'a': pd.to_datetime(['2017-01-22', '1970-01-01'])}),
     ])
     def test_pos_raises(self, df):