Make series.array read-only

Author: mroeschke

pandas/core/internals/blocks.py

@@ -2112,7 +2112,9 @@ def is_view(self) -> bool:
 
     @property
     def array_values(self) -> ExtensionArray:
-        return NumpyExtensionArray(self.values)
+        values = self.values.view()
+        values.flags.writeable = False
+        return NumpyExtensionArray(values)
 
     def get_values(self, dtype: DtypeObj | None = None) -> np.ndarray:
         if dtype == _dtype_obj:
@@ -2364,6 +2366,4 @@ def external_values(values: ArrayLike) -> ArrayLike:
         values = values.view()
         values.flags.writeable = False
 
-    # TODO(CoW) we should also mark our ExtensionArrays as read-only
-
     return values

pandas/tests/copy_view/test_array.py

@@ -141,3 +141,10 @@ def test_empty_dataframe():
     df = DataFrame()
     arr = np.asarray(df)
     assert arr.flags.writeable is True
+
+
+def test_series_array_not_writable():
+    # GH 58007
+    ser = Series([1, 2])
+    with pytest.raises(ValueError, match="assignment destination is read-only"):
+        ser.array[0] = 2