CoW: Remove copy-on-write conditions from frame tests

pandas/tests/frame/indexing/test_getitem.py

@@ -391,18 +391,13 @@ def test_getitem_empty_frame_with_boolean(self):
         df2 = df[df > 0]
         tm.assert_frame_equal(df, df2)
 
-    def test_getitem_returns_view_when_column_is_unique_in_df(
-        self, using_copy_on_write
-    ):
+    def test_getitem_returns_view_when_column_is_unique_in_df(self):
         # GH#45316
         df = DataFrame([[1, 2, 3], [4, 5, 6]], columns=["a", "a", "b"])
         df_orig = df.copy()
         view = df["b"]
         view.loc[:] = 100
-        if using_copy_on_write:
-            expected = df_orig
-        else:
-            expected = DataFrame([[1, 2, 100], [4, 5, 100]], columns=["a", "a", "b"])
+        expected = df_orig
         tm.assert_frame_equal(df, expected)
 
     def test_getitem_frozenset_unique_in_column(self):

pandas/tests/frame/indexing/test_indexing.py

@@ -565,9 +565,7 @@ def test_getitem_setitem_integer_slice_keyerrors(self):
         with pytest.raises(KeyError, match=r"^3$"):
             df2.loc[3:11] = 0
 
-    def test_fancy_getitem_slice_mixed(
-        self, float_frame, float_string_frame, using_copy_on_write
-    ):
+    def test_fancy_getitem_slice_mixed(self, float_frame, float_string_frame):
         sliced = float_string_frame.iloc[:, -3:]
         assert sliced["D"].dtype == np.float64
 
@@ -579,13 +577,7 @@ def test_fancy_getitem_slice_mixed(
         assert np.shares_memory(sliced["C"]._values, float_frame["C"]._values)
 
         sliced.loc[:, "C"] = 4.0
-        if not using_copy_on_write:
-            assert (float_frame["C"] == 4).all()
-
-            # with the enforcement of GH#45333 in 2.0, this remains a view
-            np.shares_memory(sliced["C"]._values, float_frame["C"]._values)
-        else:
-            tm.assert_frame_equal(float_frame, original)
+        tm.assert_frame_equal(float_frame, original)
 
     def test_getitem_setitem_non_ix_labels(self):
         df = DataFrame(range(20), index=date_range("2020-01-01", periods=20))
@@ -1053,7 +1045,7 @@ def test_iloc_row(self):
         expected = df.reindex(df.index[[1, 2, 4, 6]])
         tm.assert_frame_equal(result, expected)
 
-    def test_iloc_row_slice_view(self, using_copy_on_write):
+    def test_iloc_row_slice_view(self):
         df = DataFrame(
             np.random.default_rng(2).standard_normal((10, 4)), index=range(0, 20, 2)
         )
@@ -1067,11 +1059,6 @@ def test_iloc_row_slice_view(self, using_copy_on_write):
 
         exp_col = original[2].copy()
         subset.loc[:, 2] = 0.0
-        if not using_copy_on_write:
-            exp_col._values[4:8] = 0.0
-
-            # With the enforcement of GH#45333 in 2.0, this remains a view
-            assert np.shares_memory(df[2], subset[2])
         tm.assert_series_equal(df[2], exp_col)
 
     def test_iloc_col(self):
@@ -1097,32 +1084,20 @@ def test_iloc_col(self):
         expected = df.reindex(columns=df.columns[[1, 2, 4, 6]])
         tm.assert_frame_equal(result, expected)
 
-    def test_iloc_col_slice_view(self, using_copy_on_write):
+    def test_iloc_col_slice_view(self):
         df = DataFrame(
             np.random.default_rng(2).standard_normal((4, 10)), columns=range(0, 20, 2)
         )
         original = df.copy()
         subset = df.iloc[:, slice(4, 8)]
 
-        if not using_copy_on_write:
-            # verify slice is view
-            assert np.shares_memory(df[8]._values, subset[8]._values)
-
-            subset.loc[:, 8] = 0.0
-
-            assert (df[8] == 0).all()
-
-            # with the enforcement of GH#45333 in 2.0, this remains a view
-            assert np.shares_memory(df[8]._values, subset[8]._values)
-        else:
-            if using_copy_on_write:
-                # verify slice is view
-                assert np.shares_memory(df[8]._values, subset[8]._values)
-            subset[8] = 0.0
-            # subset changed
-            assert (subset[8] == 0).all()
-            # but df itself did not change (setitem replaces full column)
-            tm.assert_frame_equal(df, original)
+        # verify slice is view
+        assert np.shares_memory(df[8]._values, subset[8]._values)
+        subset[8] = 0.0
+        # subset changed
+        assert (subset[8] == 0).all()
+        # but df itself did not change (setitem replaces full column)
+        tm.assert_frame_equal(df, original)
 
     def test_loc_duplicates(self):
         # gh-17105

pandas/tests/frame/indexing/test_insert.py

@@ -71,7 +71,7 @@ def test_insert_with_columns_dups(self):
         )
         tm.assert_frame_equal(df, exp)
 
-    def test_insert_item_cache(self, using_copy_on_write):
+    def test_insert_item_cache(self):
         df = DataFrame(np.random.default_rng(2).standard_normal((4, 3)))
         ser = df[0]
         expected_warning = PerformanceWarning
@@ -80,14 +80,9 @@ def test_insert_item_cache(self, using_copy_on_write):
             for n in range(100):
                 df[n + 3] = df[1] * n
 
-        if using_copy_on_write:
-            ser.iloc[0] = 99
-            assert df.iloc[0, 0] == df[0][0]
-            assert df.iloc[0, 0] != 99
-        else:
-            ser.values[0] = 99
-            assert df.iloc[0, 0] == df[0][0]
-            assert df.iloc[0, 0] == 99
+        ser.iloc[0] = 99
+        assert df.iloc[0, 0] == df[0][0]
+        assert df.iloc[0, 0] != 99
 
     def test_insert_EA_no_warning(self):
         # PerformanceWarning about fragmented frame should not be raised when

pandas/tests/frame/indexing/test_setitem.py

@@ -324,7 +324,7 @@ def test_frame_setitem_existing_datetime64_col_other_units(self, unit):
         df["dates"] = vals
         assert (df["dates"].values == ex_vals).all()
 
-    def test_setitem_dt64tz(self, timezone_frame, using_copy_on_write):
+    def test_setitem_dt64tz(self, timezone_frame):
         df = timezone_frame
         idx = df["B"].rename("foo")
 
@@ -345,10 +345,7 @@ def test_setitem_dt64tz(self, timezone_frame, using_copy_on_write):
         tm.assert_extension_array_equal(v1, v2)
         v1base = v1._ndarray.base
         v2base = v2._ndarray.base
-        if not using_copy_on_write:
-            assert v1base is None or (id(v1base) != id(v2base))
-        else:
-            assert id(v1base) == id(v2base)
+        assert id(v1base) == id(v2base)
 
         # with nan
         df2 = df.copy()
@@ -844,7 +841,7 @@ def test_setitem_object_array_of_tzaware_datetimes(self, idx, expected):
 
 
 class TestDataFrameSetItemWithExpansion:
-    def test_setitem_listlike_views(self, using_copy_on_write):
+    def test_setitem_listlike_views(self):
         # GH#38148
         df = DataFrame({"a": [1, 2, 3], "b": [4, 4, 6]})
 
@@ -857,10 +854,7 @@ def test_setitem_listlike_views(self, using_copy_on_write):
         # edit in place the first column to check view semantics
         df.iloc[0, 0] = 100
 
-        if using_copy_on_write:
-            expected = Series([1, 2, 3], name="a")
-        else:
-            expected = Series([100, 2, 3], name="a")
+        expected = Series([1, 2, 3], name="a")
         tm.assert_series_equal(ser, expected)
 
     def test_setitem_string_column_numpy_dtype_raising(self):
@@ -870,7 +864,7 @@ def test_setitem_string_column_numpy_dtype_raising(self):
         expected = DataFrame([[1, 2, 5], [3, 4, 6]], columns=[0, 1, "0 - Name"])
         tm.assert_frame_equal(df, expected)
 
-    def test_setitem_empty_df_duplicate_columns(self, using_copy_on_write):
+    def test_setitem_empty_df_duplicate_columns(self):
         # GH#38521
         df = DataFrame(columns=["a", "b", "b"], dtype="float64")
         df.loc[:, "a"] = list(range(2))
@@ -1199,7 +1193,7 @@ def test_setitem_always_copy(self, float_frame):
         assert notna(s[5:10]).all()
 
     @pytest.mark.parametrize("consolidate", [True, False])
-    def test_setitem_partial_column_inplace(self, consolidate, using_copy_on_write):
+    def test_setitem_partial_column_inplace(self, consolidate):
         # This setting should be in-place, regardless of whether frame is
         #  single-block or multi-block
         # GH#304 this used to be incorrectly not-inplace, in which case
@@ -1215,18 +1209,11 @@ def test_setitem_partial_column_inplace(self, consolidate, using_copy_on_write):
         else:
             assert len(df._mgr.blocks) == 2
 
-        zvals = df["z"]._values
-
         df.loc[2:, "z"] = 42
 
         expected = Series([np.nan, np.nan, 42, 42], index=df.index, name="z")
         tm.assert_series_equal(df["z"], expected)
 
-        # check setting occurred in-place
-        if not using_copy_on_write:
-            tm.assert_numpy_array_equal(zvals, expected.values)
-            assert np.shares_memory(zvals, df["z"]._values)
-
     def test_setitem_duplicate_columns_not_inplace(self):
         # GH#39510
         cols = ["A", "B"] * 2
@@ -1298,7 +1285,7 @@ def test_setitem_not_operating_inplace(self, value, set_value, indexer):
         df[indexer] = set_value
         tm.assert_frame_equal(view, expected)
 
-    def test_setitem_column_update_inplace(self, using_copy_on_write):
+    def test_setitem_column_update_inplace(self):
         # https://github.com/pandas-dev/pandas/issues/47172
 
         labels = [f"c{i}" for i in range(10)]
@@ -1308,12 +1295,8 @@ def test_setitem_column_update_inplace(self, using_copy_on_write):
         with tm.raises_chained_assignment_error():
             for label in df.columns:
                 df[label][label] = 1
-        if not using_copy_on_write:
-            # diagonal values all updated
-            assert np.all(values[np.arange(10), np.arange(10)] == 1)
-        else:
-            # original dataframe not updated
-            assert np.all(values[np.arange(10), np.arange(10)] == 0)
+        # original dataframe not updated
+        assert np.all(values[np.arange(10), np.arange(10)] == 0)
 
     def test_setitem_column_frame_as_category(self):
         # GH31581

pandas/tests/frame/indexing/test_xs.py

@@ -58,7 +58,7 @@ def test_xs_dt_error(self, datetime_frame):
         ):
             datetime_frame.xs(datetime_frame.index[0] - BDay())
 
-    def test_xs_other(self, float_frame, using_copy_on_write):
+    def test_xs_other(self, float_frame):
         float_frame_orig = float_frame.copy()
         # xs get column
         series = float_frame.xs("A", axis=1)
@@ -68,12 +68,9 @@ def test_xs_other(self, float_frame, using_copy_on_write):
         # view is returned if possible
         series = float_frame.xs("A", axis=1)
         series[:] = 5
-        if using_copy_on_write:
-            # but with CoW the view shouldn't propagate mutations
-            tm.assert_series_equal(float_frame["A"], float_frame_orig["A"])
-            assert not (expected == 5).all()
-        else:
-            assert (expected == 5).all()
+        # The view shouldn't propagate mutations
+        tm.assert_series_equal(float_frame["A"], float_frame_orig["A"])
+        assert not (expected == 5).all()
 
     def test_xs_corner(self):
         # pathological mixed-type reordering case
@@ -363,34 +360,23 @@ def test_xs_droplevel_false(self):
         expected = DataFrame({"a": [1]})
         tm.assert_frame_equal(result, expected)
 
-    def test_xs_droplevel_false_view(self, using_copy_on_write):
+    def test_xs_droplevel_false_view(self):
         # GH#37832
         df = DataFrame([[1, 2, 3]], columns=Index(["a", "b", "c"]))
         result = df.xs("a", axis=1, drop_level=False)
         # check that result still views the same data as df
         assert np.shares_memory(result.iloc[:, 0]._values, df.iloc[:, 0]._values)
 
         df.iloc[0, 0] = 2
-        if using_copy_on_write:
-            # with copy on write the subset is never modified
-            expected = DataFrame({"a": [1]})
-        else:
-            # modifying original df also modifies result when having a single block
-            expected = DataFrame({"a": [2]})
+        # The subset is never modified
+        expected = DataFrame({"a": [1]})
         tm.assert_frame_equal(result, expected)
 
-        # with mixed dataframe, modifying the parent doesn't modify result
-        # TODO the "split" path behaves differently here as with single block
         df = DataFrame([[1, 2.5, "a"]], columns=Index(["a", "b", "c"]))
         result = df.xs("a", axis=1, drop_level=False)
         df.iloc[0, 0] = 2
-        if using_copy_on_write:
-            # with copy on write the subset is never modified
-            expected = DataFrame({"a": [1]})
-        else:
-            # FIXME: iloc does not update the array inplace using
-            # "split" path
-            expected = DataFrame({"a": [1]})
+        # The subset is never modified
+        expected = DataFrame({"a": [1]})
         tm.assert_frame_equal(result, expected)
 
     def test_xs_list_indexer_droplevel_false(self):

pandas/tests/frame/methods/test_align.py

@@ -48,15 +48,12 @@ def test_frame_align_aware(self):
         assert new1.index.tz is timezone.utc
         assert new2.index.tz is timezone.utc
 
-    def test_align_float(self, float_frame, using_copy_on_write):
+    def test_align_float(self, float_frame):
         af, bf = float_frame.align(float_frame)
         assert af._mgr is not float_frame._mgr
 
         af, bf = float_frame.align(float_frame, copy=False)
-        if not using_copy_on_write:
-            assert af._mgr is float_frame._mgr
-        else:
-            assert af._mgr is not float_frame._mgr
+        assert af._mgr is not float_frame._mgr
 
         # axis = 0
         other = float_frame.iloc[:-5, :3]

pandas/tests/frame/methods/test_cov_corr.py

@@ -207,7 +207,7 @@ def test_corr_nullable_integer(self, nullable_column, other_column, method):
         expected = DataFrame(np.ones((2, 2)), columns=["a", "b"], index=["a", "b"])
         tm.assert_frame_equal(result, expected)
 
-    def test_corr_item_cache(self, using_copy_on_write):
+    def test_corr_item_cache(self):
         # Check that corr does not lead to incorrect entries in item_cache
 
         df = DataFrame({"A": range(10)})
@@ -218,15 +218,8 @@ def test_corr_item_cache(self, using_copy_on_write):
 
         _ = df.corr(numeric_only=True)
 
-        if using_copy_on_write:
-            ser.iloc[0] = 99
-            assert df.loc[0, "A"] == 0
-        else:
-            # Check that the corr didn't break link between ser and df
-            ser.values[0] = 99
-            assert df.loc[0, "A"] == 99
-            assert df["A"] is ser
-            assert df.values[0, 0] == 99
+        ser.iloc[0] = 99
+        assert df.loc[0, "A"] == 0
 
     @pytest.mark.parametrize("length", [2, 20, 200, 2000])
     def test_corr_for_constant_columns(self, length):