BUG: Series add casting to object for list and masked series (#50762)

phofl · web-flow · commit f63e7b82177e · 2023-01-17T09:53:28.000-08:00
* BUG: Series add casting to object for list and masked series

* Fix boolean

* Fix length missmatch
diff --git a/doc/source/whatsnew/v2.0.0.rst b/doc/source/whatsnew/v2.0.0.rst
@@ -931,6 +931,7 @@ Numeric
 - Bug in arithmetic operations on :class:`Series` not propagating mask when combining masked dtypes and numpy dtypes (:issue:`45810`, :issue:`42630`)
 - Bug in DataFrame reduction methods (e.g. :meth:`DataFrame.sum`) with object dtype, ``axis=1`` and ``numeric_only=False`` would not be coerced to float (:issue:`49551`)
 - Bug in :meth:`DataFrame.sem` and :meth:`Series.sem` where an erroneous ``TypeError`` would always raise when using data backed by an :class:`ArrowDtype` (:issue:`49759`)
+- Bug in :meth:`Series.__add__` casting to object for list and masked :class:`Series` (:issue:`22962`)
 
 Conversion
 ^^^^^^^^^^
diff --git a/pandas/core/arrays/masked.py b/pandas/core/arrays/masked.py
@@ -621,6 +621,27 @@ def _arith_method(self, other, op):
         op_name = op.__name__
         omask = None
 
+        if (
+            not hasattr(other, "dtype")
+            and is_list_like(other)
+            and len(other) == len(self)
+        ):
+            # Try inferring masked dtype instead of casting to object
+            inferred_dtype = lib.infer_dtype(other, skipna=True)
+            if inferred_dtype == "integer":
+                from pandas.core.arrays import IntegerArray
+
+                other = IntegerArray._from_sequence(other)
+            elif inferred_dtype in ["floating", "mixed-integer-float"]:
+                from pandas.core.arrays import FloatingArray
+
+                other = FloatingArray._from_sequence(other)
+
+            elif inferred_dtype in ["boolean"]:
+                from pandas.core.arrays import BooleanArray
+
+                other = BooleanArray._from_sequence(other)
+
         if isinstance(other, BaseMaskedArray):
             other, omask = other._data, other._mask
 
diff --git a/pandas/tests/series/test_arithmetic.py b/pandas/tests/series/test_arithmetic.py
@@ -325,6 +325,27 @@ def test_mask_div_propagate_na_for_non_na_dtype(self):
         result = ser2 / ser1
         tm.assert_series_equal(result, expected)
 
+    @pytest.mark.parametrize("val, dtype", [(3, "Int64"), (3.5, "Float64")])
+    def test_add_list_to_masked_array(self, val, dtype):
+        # GH#22962
+        ser = Series([1, None, 3], dtype="Int64")
+        result = ser + [1, None, val]
+        expected = Series([2, None, 3 + val], dtype=dtype)
+        tm.assert_series_equal(result, expected)
+
+        result = [1, None, val] + ser
+        tm.assert_series_equal(result, expected)
+
+    def test_add_list_to_masked_array_boolean(self):
+        # GH#22962
+        ser = Series([True, None, False], dtype="boolean")
+        result = ser + [True, None, True]
+        expected = Series([True, None, True], dtype="boolean")
+        tm.assert_series_equal(result, expected)
+
+        result = [True, None, True] + ser
+        tm.assert_series_equal(result, expected)
+
 
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