BUG: TimedeltaArray - Index result.name (#27962)

* BUG: TimedeltaArray - Index result.name

* change assert to TypeErrror

Author: jbrockmendel

pandas/core/indexes/base.py

@@ -2325,7 +2325,10 @@ def __sub__(self, other):
         return Index(np.array(self) - other)
 
     def __rsub__(self, other):
-        return Index(other - np.array(self))
+        # wrap Series to ensure we pin name correctly
+        from pandas import Series
+
+        return Index(other - Series(self))
 
     def __and__(self, other):
         return self.intersection(other)

pandas/core/ops/array_ops.py

@@ -74,8 +74,9 @@ def masked_arith_op(x, y, op):
                 result[mask] = op(xrav[mask], yrav[mask])
 
     else:
-        assert is_scalar(y), type(y)
-        assert isinstance(x, np.ndarray), type(x)
+        if not is_scalar(y):
+            raise TypeError(type(y))
+
         # mask is only meaningful for x
         result = np.empty(x.size, dtype=x.dtype)
         mask = notna(xrav)

pandas/tests/arithmetic/test_timedelta64.py

@@ -1378,8 +1378,12 @@ def test_td64arr_add_offset_array(self, box):
     @pytest.mark.parametrize(
         "names", [(None, None, None), ("foo", "bar", None), ("foo", "foo", "foo")]
     )
-    def test_td64arr_sub_offset_index(self, names, box):
+    def test_td64arr_sub_offset_index(self, names, box_with_array):
         # GH#18824, GH#19744
+        box = box_with_array
+        xbox = box if box is not tm.to_array else pd.Index
+        exname = names[2] if box is not tm.to_array else names[1]
+
         if box is pd.DataFrame and names[1] == "bar":
             pytest.skip(
                 "Name propagation for DataFrame does not behave like "
@@ -1390,11 +1394,11 @@ def test_td64arr_sub_offset_index(self, names, box):
         other = pd.Index([pd.offsets.Hour(n=1), pd.offsets.Minute(n=-2)], name=names[1])
 
         expected = TimedeltaIndex(
-            [tdi[n] - other[n] for n in range(len(tdi))], freq="infer", name=names[2]
+            [tdi[n] - other[n] for n in range(len(tdi))], freq="infer", name=exname
         )
 
         tdi = tm.box_expected(tdi, box)
-        expected = tm.box_expected(expected, box)
+        expected = tm.box_expected(expected, xbox)
 
         # The DataFrame operation is transposed and so operates as separate
         #  scalar operations, which do not issue a PerformanceWarning