TST: Test cow for set_flags

pandas-dev · phofl · Jan 3, 2023 · Dec 29, 2022 · Dec 29, 2022 · Jan 3, 2023
commit 83edb2926a7d34165236f544cfc4b32ec6157b59
diff --git a/pandas/conftest.py b/pandas/conftest.py
@@ -1903,6 +1903,7 @@ def using_copy_on_write() -> bool:
     """
     Fixture to check if Copy-on-Write is enabled.
     """
+    pd.options.mode.copy_on_write = True
     return pd.options.mode.copy_on_write and pd.options.mode.data_manager == "block"
 
 

diff --git a/pandas/core/generic.py b/pandas/core/generic.py
@@ -405,6 +405,8 @@ def set_flags(
 
         Parameters
         ----------
+        copy : bool, default False
+            Specify if a copy of the object should be made.
         allows_duplicate_labels : bool, optional
             Whether the returned object allows duplicate labels.
 

diff --git a/pandas/tests/copy_view/test_methods.py b/pandas/tests/copy_view/test_methods.py
@@ -456,3 +456,21 @@ def test_series_set_axis(using_copy_on_write):
     ser2.iloc[0] = 0
     assert not np.shares_memory(ser2, ser)
     tm.assert_series_equal(ser, ser_orig)
+
+
+def test_set_flags(using_copy_on_write):
+    ser = Series([1, 2, 3])
+    ser_orig = ser.copy()
+    ser2 = ser.set_flags(allows_duplicate_labels=False)
+
+    assert np.shares_memory(ser, ser2)
+
+    # mutating ser triggers a copy-on-write for the column / block
+    ser2.iloc[0] = 0
+    if using_copy_on_write:
+        assert not np.shares_memory(ser2, ser)
+        tm.assert_series_equal(ser, ser_orig)
+    else:
+        assert np.shares_memory(ser2, ser)
+        expected = Series([0, 2, 3])
+        tm.assert_series_equal(ser, expected)
-Original file line number
+Diff line change
@@ Expand Up / @@ -1903,6 +1903,7 @@ def using_copy_on_write() -> bool: @@
         """
         Fixture to check if Copy-on-Write is enabled.
         """
+        pd.options.mode.copy_on_write = True
         return pd.options.mode.copy_on_write and pd.options.mode.data_manager == "block"
@@ Expand Down @@