BUG: frame.mask(foo, bar, inplace=True) with EAs incorrectly raising

doc/source/whatsnew/v1.5.0.rst

@@ -263,6 +263,7 @@ Indexing
 - Bug when setting a value too large for a :class:`Series` dtype failing to coerce to a common type (:issue:`26049`, :issue:`32878`)
 - Bug in :meth:`Series.__setitem__` when setting ``boolean`` dtype values containing ``NA`` incorrectly raising instead of casting to ``boolean`` dtype (:issue:`45462`)
 - Bug in :meth:`Series.__setitem__` where setting :attr:`NA` into a numeric-dtpye :class:`Series` would incorrectly upcast to object-dtype rather than treating the value as ``np.nan`` (:issue:`44199`)
+- Bug in :meth:`DataFrame.mask` with ``inplace=True`` and ``ExtensionDtype`` columns incorrectly raising (:issue:`45577`)
 - Bug in getting a column from a DataFrame with an object-dtype row index with datetime-like values: the resulting Series now preserves the exact object-dtype Index from the parent DataFrame (:issue:`42950`)
 -
 

pandas/core/internals/blocks.py

@@ -1436,6 +1436,7 @@ def putmask(self, mask, new) -> list[Block]:
 
         values = self.values
 
+        new = self._maybe_squeeze_arg(new)
         mask = self._maybe_squeeze_arg(mask)
 
         try:

pandas/tests/extension/base/methods.py

@@ -443,7 +443,8 @@ def test_where_series(self, data, na_value, as_frame):
         cls = type(data)
         a, b = data[:2]
 
-        ser = pd.Series(cls._from_sequence([a, a, b, b], dtype=data.dtype))
+        orig = pd.Series(cls._from_sequence([a, a, b, b], dtype=data.dtype))
+        ser = orig.copy()
         cond = np.array([True, True, False, False])
 
         if as_frame:
@@ -459,7 +460,13 @@ def test_where_series(self, data, na_value, as_frame):
             expected = expected.to_frame(name="a")
         self.assert_equal(result, expected)
 
+        ser.mask(~cond, inplace=True)
+        self.assert_equal(ser, expected)
+
         # array other
+        ser = orig.copy()
+        if as_frame:
+            ser = ser.to_frame(name="a")
         cond = np.array([True, False, True, True])
         other = cls._from_sequence([a, b, a, b], dtype=data.dtype)
         if as_frame:
@@ -471,6 +478,9 @@ def test_where_series(self, data, na_value, as_frame):
             expected = expected.to_frame(name="a")
         self.assert_equal(result, expected)
 
+        ser.mask(~cond, other, inplace=True)
+        self.assert_equal(ser, expected)
+
     @pytest.mark.parametrize("repeats", [0, 1, 2, [1, 2, 3]])
     def test_repeat(self, data, repeats, as_series, use_numpy):
         arr = type(data)._from_sequence(data[:3], dtype=data.dtype)

pandas/tests/frame/indexing/test_where.py

@@ -812,6 +812,12 @@ def test_where_string_dtype(frame_or_series):
     )
     tm.assert_equal(result, expected)
 
+    result = obj.mask(~filter_ser, filtered_obj)
+    tm.assert_equal(result, expected)
+
+    obj.mask(~filter_ser, filtered_obj, inplace=True)
+    tm.assert_equal(result, expected)
+
 
 def test_where_bool_comparison():
     # GH 10336