Backport PR #51832 on branch 2.0.x (BUG / CoW: Series.view not respecting CoW) (#51937)

Backport PR #51832: BUG / CoW: Series.view not respecting CoW

Co-authored-by: Patrick Hoefler <[email protected]>

Author: meeseeksmachine

doc/source/whatsnew/v2.0.0.rst

@@ -221,6 +221,8 @@ Copy-on-Write improvements
 - Arithmetic operations that can be inplace, e.g. ``ser *= 2`` will now respect the
   Copy-on-Write mechanism.
 
+- :meth:`Series.view` will now respect the Copy-on-Write mechanism.
+
 Copy-on-Write can be enabled through one of
 
 .. code-block:: python

pandas/core/series.py

@@ -840,6 +840,10 @@ def view(self, dtype: Dtype | None = None) -> Series:
         #  implementation
         res_values = self.array.view(dtype)
         res_ser = self._constructor(res_values, index=self.index)
+        if isinstance(res_ser._mgr, SingleBlockManager) and using_copy_on_write():
+            blk = res_ser._mgr._block
+            blk.refs = cast("BlockValuesRefs", self._references)
+            blk.refs.add_reference(blk)  # type: ignore[arg-type]
         return res_ser.__finalize__(self, method="view")
 
     # ----------------------------------------------------------------------

pandas/tests/copy_view/test_methods.py

@@ -1672,3 +1672,21 @@ def test_transpose_ea_single_column(using_copy_on_write):
     result = df.T
 
     assert not np.shares_memory(get_array(df, "a"), get_array(result, 0))
+
+
+def test_series_view(using_copy_on_write):
+    ser = Series([1, 2, 3])
+    ser_orig = ser.copy()
+
+    ser2 = ser.view()
+    assert np.shares_memory(get_array(ser), get_array(ser2))
+    if using_copy_on_write:
+        assert not ser2._mgr._has_no_reference(0)
+
+    ser2.iloc[0] = 100
+
+    if using_copy_on_write:
+        tm.assert_series_equal(ser_orig, ser)
+    else:
+        expected = Series([100, 2, 3])
+        tm.assert_series_equal(ser, expected)