BUG: Arithmetic operation on ExtensionArray (pandas-dev#62471)

Author: praateekmahajan

doc/source/whatsnew/v3.0.0.rst

@@ -1208,6 +1208,7 @@ ExtensionArray
 - Bug in comparison between object with :class:`ArrowDtype` and incompatible-dtyped (e.g. string vs bool) incorrectly raising instead of returning all-``False`` (for ``==``) or all-``True`` (for ``!=``) (:issue:`59505`)
 - Bug in constructing pandas data structures when passing into ``dtype`` a string of the type followed by ``[pyarrow]`` while PyArrow is not installed would raise ``NameError`` rather than ``ImportError`` (:issue:`57928`)
 - Bug in various :class:`DataFrame` reductions for pyarrow temporal dtypes returning incorrect dtype when result was null (:issue:`59234`)
+- Fixed flex arithmetic with :class:`ExtensionArray` operands raising when ``fill_value`` was passed. (:issue:`62467`)
 
 Styler
 ^^^^^^

pandas/core/series.py

@@ -6738,7 +6738,7 @@ def _flex_method(self, other, op, *, level=None, fill_value=None, axis: Axis = 0
 
         if isinstance(other, Series):
             return self._binop(other, op, level=level, fill_value=fill_value)
-        elif isinstance(other, (np.ndarray, list, tuple)):
+        elif isinstance(other, (np.ndarray, list, tuple, ExtensionArray)):
             if len(other) != len(self):
                 raise ValueError("Lengths must be equal")
             other = self._constructor(other, self.index, copy=False)

pandas/tests/series/test_arithmetic.py

@@ -160,6 +160,28 @@ def _check_fill(meth, op, a, b, fill_value=0):
         # should accept axis=0 or axis='rows'
         op(a, b, axis=0)
 
+    @pytest.mark.parametrize("kind", ["datetime", "timedelta"])
+    def test_rhs_extension_array_sub_with_fill_value(self, kind):
+        # GH:62467
+        if kind == "datetime":
+            left = Series(
+                [pd.Timestamp("2025-08-20"), pd.Timestamp("2025-08-21")],
+                dtype=np.dtype("datetime64[ns]"),
+            )
+        else:
+            left = Series(
+                [Timedelta(days=1), Timedelta(days=2)],
+                dtype=np.dtype("timedelta64[ns]"),
+            )
+
+        right = (
+            left._values
+        )  # DatetimeArray or TimedeltaArray which is an ExtensionArray
+
+        result = left.sub(right, fill_value=left.iloc[0])
+        expected = Series(np.zeros(len(left), dtype=np.dtype("timedelta64[ns]")))
+        tm.assert_series_equal(result, expected)
+
     def test_flex_disallows_dataframe(self):
         # GH#46179
         df = pd.DataFrame(
@@ -430,6 +452,22 @@ def test_comparison_flex_alignment(self, values, op):
         expected = Series(values, index=list("abcd"))
         tm.assert_series_equal(result, expected)
 
+    @pytest.mark.parametrize(
+        "left",
+        [
+            Series(Categorical(["a", "b", "a"])),
+            Series(pd.period_range("2020Q1", periods=3, freq="Q")),
+        ],
+        ids=["categorical", "period"],
+    )
+    def test_rhs_extension_array_eq_with_fill_value(self, left):
+        # GH:#62467
+        right = left._values  # this is an ExtensionArray
+
+        result = left.eq(right, fill_value=left.iloc[0])
+        expected = Series([True, True, True])
+        tm.assert_series_equal(result, expected)
+
     @pytest.mark.parametrize(
         "values, op, fill_value",
         [