Backport PR #52060 on branch 2.0.x (API CoW: Return read_only NumPy a…

…rray from ravel) (#52273)

Backport PR #52060: API CoW: Return read_only NumPy array from ravel

Co-authored-by: Patrick Hoefler <61934744+phofl@users.noreply.github.com>

pandas/core/series.py

@@ -772,7 +772,10 @@ def ravel(self, order: str = "C") -> ArrayLike:
         --------
         numpy.ndarray.ravel : Return a flattened array.
         """
-        return self._values.ravel(order=order)
+        arr = self._values.ravel(order=order)
+        if isinstance(arr, np.ndarray) and using_copy_on_write():
+            arr.flags.writeable = False
+        return arr
 
     def __len__(self) -> int:
         """

pandas/tests/copy_view/test_array.py

@@ -110,3 +110,12 @@ def test_series_to_numpy(using_copy_on_write):
     arr = ser.to_numpy(dtype="float64")
     assert not np.shares_memory(arr, get_array(ser, "name"))
     assert arr.flags.writeable is True
+
+
+@pytest.mark.parametrize("order", ["F", "C"])
+def test_ravel_read_only(using_copy_on_write, order):
+    ser = Series([1, 2, 3])
+    arr = ser.ravel(order=order)
+    if using_copy_on_write:
+        assert arr.flags.writeable is False
+    assert np.shares_memory(get_array(ser), arr)