BUG: indexing raises for ea into numpy series (#55633)

pandas-dev · Oct 23, 2023 · 03a4981 · 03a4981
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diff --git a/doc/source/whatsnew/v2.2.0.rst b/doc/source/whatsnew/v2.2.0.rst
@@ -345,9 +345,9 @@ Interval
 
 Indexing
 ^^^^^^^^
+- Bug in :meth:`DataFrame.loc` when setting :class:`Series` with extension dtype into NumPy dtype (:issue:`55604`)
 - Bug in :meth:`Index.difference` not returning a unique set of values when ``other`` is empty or ``other`` is considered non-comparable (:issue:`55113`)
 - Bug in setting :class:`Categorical` values into a :class:`DataFrame` with numpy dtypes raising ``RecursionError`` (:issue:`52927`)
--
 
 Missing
 ^^^^^^^

diff --git a/pandas/core/dtypes/cast.py b/pandas/core/dtypes/cast.py
@@ -1816,7 +1816,8 @@ def np_can_hold_element(dtype: np.dtype, element: Any) -> Any:
             if not isinstance(tipo, np.dtype):
                 # i.e. nullable IntegerDtype; we can put this into an ndarray
                 #  losslessly iff it has no NAs
-                if element._hasna:
+                arr = element._values if isinstance(element, ABCSeries) else element
+                if arr._hasna:
                     raise LossySetitemError
                 return element
 

diff --git a/pandas/tests/frame/indexing/test_setitem.py b/pandas/tests/frame/indexing/test_setitem.py
@@ -761,6 +761,17 @@ def test_setitem_frame_midx_columns(self):
         df[col_name] = df[[col_name]]
         tm.assert_frame_equal(df, expected)
 
+    def test_loc_setitem_ea_dtype(self):
+        # GH#55604
+        df = DataFrame({"a": np.array([10], dtype="i8")})
+        df.loc[:, "a"] = Series([11], dtype="Int64")
+        expected = DataFrame({"a": np.array([11], dtype="i8")})
+        tm.assert_frame_equal(df, expected)
+
+        df = DataFrame({"a": np.array([10], dtype="i8")})
+        df.iloc[:, 0] = Series([11], dtype="Int64")
+        tm.assert_frame_equal(df, expected)
+
 
 class TestSetitemTZAwareValues:
     @pytest.fixture