__setitem__ raises NotImplemented when bool mask passed through iloc

Author: arthurlw

pandas/core/indexing.py

@@ -1637,6 +1637,18 @@ def _has_valid_setitem_indexer(self, indexer) -> bool:
                 "Consider using .loc with a DataFrame indexer for automatic alignment.",
             )
 
+        # Check for Series boolean indexer
+        if com.is_bool_indexer(indexer) and hasattr(indexer, "index") and isinstance(indexer.index, Index):
+            if indexer.index.inferred_type == "integer":
+                raise NotImplementedError(
+                    "iLocation based boolean "
+                    "indexing on an integer type "
+                    "is not available"
+                )
+            raise ValueError(
+                "iLocation based boolean indexing cannot use an indexable as a mask"
+            )
+
         if not isinstance(indexer, tuple):
             indexer = _tuplify(self.ndim, indexer)
 

pandas/tests/frame/indexing/test_getitem.py

@@ -407,6 +407,19 @@ def test_getitem_frozenset_unique_in_column(self):
         expected = Series([1], name=frozenset(["KEY"]))
         tm.assert_series_equal(result, expected)
 
+    def test_series_boolean_indexer_iloc_consistency(self):
+    # GH#60994 - Test consistency between __getitem__ and __setitem__ for Series boolean indexers
+        ser = Series([0, 1, 2])
+        mask = Series([True, False, False])
+        
+        # __getitem__ should raise NotImplementedError
+        with pytest.raises(NotImplementedError, match="iLocation based boolean indexing on an integer type is not available"):
+            ser.iloc[mask]
+            
+        # __setitem__ should also raise NotImplementedError for consistency
+        with pytest.raises(NotImplementedError, match="iLocation based boolean indexing on an integer type is not available"):
+            ser.iloc[mask] = 10
+
 
 class TestGetitemSlice:
     def test_getitem_slice_float64(self, frame_or_series):