Backport PR #51464 on branch 2.0.x (CoW: Ignore copy=True when copy_o…

…n_write is enabled) (#51849)

Backport PR #51464: CoW: Ignore copy=True when copy_on_write is enabled

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

pandas/core/frame.py

@@ -11028,7 +11028,7 @@ def to_timestamp(
         >>> df2.index
         DatetimeIndex(['2023-01-31', '2024-01-31'], dtype='datetime64[ns]', freq=None)
         """
-        new_obj = self.copy(deep=copy)
+        new_obj = self.copy(deep=copy and not using_copy_on_write())
 
         axis_name = self._get_axis_name(axis)
         old_ax = getattr(self, axis_name)
@@ -11085,7 +11085,7 @@ def to_period(
         >>> idx.to_period("Y")
         PeriodIndex(['2001', '2002', '2003'], dtype='period[A-DEC]')
         """
-        new_obj = self.copy(deep=copy)
+        new_obj = self.copy(deep=copy and not using_copy_on_write())
 
         axis_name = self._get_axis_name(axis)
         old_ax = getattr(self, axis_name)

pandas/core/generic.py

@@ -442,7 +442,7 @@ def set_flags(
         >>> df2.flags.allows_duplicate_labels
         False
         """
-        df = self.copy(deep=copy)
+        df = self.copy(deep=copy and not using_copy_on_write())
         if allows_duplicate_labels is not None:
             df.flags["allows_duplicate_labels"] = allows_duplicate_labels
         return df
@@ -713,7 +713,7 @@ def _set_axis_nocheck(
         else:
             # With copy=False, we create a new object but don't copy the
             #  underlying data.
-            obj = self.copy(deep=copy)
+            obj = self.copy(deep=copy and not using_copy_on_write())
             setattr(obj, obj._get_axis_name(axis), labels)
             return obj
 
@@ -742,7 +742,7 @@ def swapaxes(
         j = self._get_axis_number(axis2)
 
         if i == j:
-            return self.copy(deep=copy)
+            return self.copy(deep=copy and not using_copy_on_write())
 
         mapping = {i: j, j: i}
 
@@ -999,7 +999,7 @@ def _rename(
                 index = mapper
 
         self._check_inplace_and_allows_duplicate_labels(inplace)
-        result = self if inplace else self.copy(deep=copy)
+        result = self if inplace else self.copy(deep=copy and not using_copy_on_write())
 
         for axis_no, replacements in enumerate((index, columns)):
             if replacements is None:
@@ -1215,6 +1215,9 @@ class  name
 
         inplace = validate_bool_kwarg(inplace, "inplace")
 
+        if copy and using_copy_on_write():
+            copy = False
+
         if mapper is not lib.no_default:
             # Use v0.23 behavior if a scalar or list
             non_mapper = is_scalar(mapper) or (
@@ -5322,6 +5325,8 @@ def reindex(
 
         # if all axes that are requested to reindex are equal, then only copy
         # if indicated must have index names equal here as well as values
+        if copy and using_copy_on_write():
+            copy = False
         if all(
             self._get_axis(axis_name).identical(ax)
             for axis_name, ax in axes.items()
@@ -5416,10 +5421,14 @@ def _reindex_with_indexers(
             # If we've made a copy once, no need to make another one
             copy = False
 
-        if (copy or copy is None) and new_data is self._mgr:
+        if (
+            (copy or copy is None)
+            and new_data is self._mgr
+            and not using_copy_on_write()
+        ):
             new_data = new_data.copy(deep=copy)
         elif using_copy_on_write() and new_data is self._mgr:
-            new_data = new_data.copy(deep=copy)
+            new_data = new_data.copy(deep=False)
 
         return self._constructor(new_data).__finalize__(self)
 
@@ -6239,6 +6248,9 @@ def astype(
         2   2020-01-03
         dtype: datetime64[ns]
         """
+        if copy and using_copy_on_write():
+            copy = False
+
         if is_dict_like(dtype):
             if self.ndim == 1:  # i.e. Series
                 if len(dtype) > 1 or self.name not in dtype:
@@ -9499,6 +9511,8 @@ def _align_series(
         fill_axis: Axis = 0,
     ):
         is_series = isinstance(self, ABCSeries)
+        if copy and using_copy_on_write():
+            copy = False
 
         if (not is_series and axis is None) or axis not in [None, 0, 1]:
             raise ValueError("Must specify axis=0 or 1")
@@ -10261,8 +10275,7 @@ def truncate(
         if isinstance(ax, MultiIndex):
             setattr(result, self._get_axis_name(axis), ax.truncate(before, after))
 
-        if copy or (copy is None and not using_copy_on_write()):
-            result = result.copy(deep=copy)
+        result = result.copy(deep=copy and not using_copy_on_write())
 
         return result
 
@@ -10343,7 +10356,7 @@ def _tz_convert(ax, tz):
                 raise ValueError(f"The level {level} is not valid")
             ax = _tz_convert(ax, tz)
 
-        result = self.copy(deep=copy)
+        result = self.copy(deep=copy and not using_copy_on_write())
         result = result.set_axis(ax, axis=axis, copy=False)
         return result.__finalize__(self, method="tz_convert")
 
@@ -10525,7 +10538,7 @@ def _tz_localize(ax, tz, ambiguous, nonexistent):
                 raise ValueError(f"The level {level} is not valid")
             ax = _tz_localize(ax, tz, ambiguous, nonexistent)
 
-        result = self.copy(deep=copy)
+        result = self.copy(deep=copy and not using_copy_on_write())
         result = result.set_axis(ax, axis=axis, copy=False)
         return result.__finalize__(self, method="tz_localize")
 

pandas/core/internals/managers.py

@@ -442,6 +442,8 @@ def astype(self: T, dtype, copy: bool | None = False, errors: str = "raise") ->
                 copy = False
             else:
                 copy = True
+        elif using_copy_on_write():
+            copy = False
 
         return self.apply(
             "astype",
@@ -457,6 +459,8 @@ def convert(self: T, copy: bool | None) -> T:
                 copy = False
             else:
                 copy = True
+        elif using_copy_on_write():
+            copy = False
 
         return self.apply("convert", copy=copy, using_cow=using_copy_on_write())
 

pandas/core/reshape/concat.py

@@ -366,6 +366,8 @@ def concat(
             copy = False
         else:
             copy = True
+    elif copy and using_copy_on_write():
+        copy = False
 
     op = _Concatenator(
         objs,

pandas/core/series.py

@@ -4129,7 +4129,7 @@ def swaplevel(
         {examples}
         """
         assert isinstance(self.index, MultiIndex)
-        result = self.copy(deep=copy)
+        result = self.copy(deep=copy and not using_copy_on_write())
         result.index = self.index.swaplevel(i, j)
         return result
 
@@ -5743,7 +5743,7 @@ def to_timestamp(
         if not isinstance(self.index, PeriodIndex):
             raise TypeError(f"unsupported Type {type(self.index).__name__}")
 
-        new_obj = self.copy(deep=copy)
+        new_obj = self.copy(deep=copy and not using_copy_on_write())
         new_index = self.index.to_timestamp(freq=freq, how=how)
         setattr(new_obj, "index", new_index)
         return new_obj
@@ -5783,7 +5783,7 @@ def to_period(self, freq: str | None = None, copy: bool | None = None) -> Series
         if not isinstance(self.index, DatetimeIndex):
             raise TypeError(f"unsupported Type {type(self.index).__name__}")
 
-        new_obj = self.copy(deep=copy)
+        new_obj = self.copy(deep=copy and not using_copy_on_write())
         new_index = self.index.to_period(freq=freq)
         setattr(new_obj, "index", new_index)
         return new_obj

pandas/tests/copy_view/test_functions.py

@@ -181,6 +181,21 @@ def test_concat_mixed_series_frame(using_copy_on_write):
     tm.assert_frame_equal(result, expected)
 
 
+@pytest.mark.parametrize("copy", [True, None, False])
+def test_concat_copy_keyword(using_copy_on_write, copy):
+    df = DataFrame({"a": [1, 2]})
+    df2 = DataFrame({"b": [1.5, 2.5]})
+
+    result = concat([df, df2], axis=1, copy=copy)
+
+    if using_copy_on_write or copy is False:
+        assert np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+        assert np.shares_memory(get_array(df2, "b"), get_array(result, "b"))
+    else:
+        assert not np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+        assert not np.shares_memory(get_array(df2, "b"), get_array(result, "b"))
+
+
 @pytest.mark.parametrize(
     "func",
     [
@@ -280,3 +295,18 @@ def test_merge_on_key_enlarging_one(using_copy_on_write, func, how):
         assert not np.shares_memory(get_array(result, "a"), get_array(df1, "a"))
     tm.assert_frame_equal(df1, df1_orig)
     tm.assert_frame_equal(df2, df2_orig)
+
+
+@pytest.mark.parametrize("copy", [True, None, False])
+def test_merge_copy_keyword(using_copy_on_write, copy):
+    df = DataFrame({"a": [1, 2]})
+    df2 = DataFrame({"b": [3, 4.5]})
+
+    result = df.merge(df2, copy=copy, left_index=True, right_index=True)
+
+    if using_copy_on_write or copy is False:
+        assert np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+        assert np.shares_memory(get_array(df2, "b"), get_array(result, "b"))
+    else:
+        assert not np.shares_memory(get_array(df, "a"), get_array(result, "a"))
+        assert not np.shares_memory(get_array(df2, "b"), get_array(result, "b"))

pandas/tests/copy_view/test_methods.py

@@ -66,6 +66,7 @@ def test_copy_shallow(using_copy_on_write):
         lambda df, copy: df.rename(columns=str.lower, copy=copy),
         lambda df, copy: df.reindex(columns=["a", "c"], copy=copy),
         lambda df, copy: df.reindex_like(df, copy=copy),
+        lambda df, copy: df.align(df, copy=copy)[0],
         lambda df, copy: df.set_axis(["a", "b", "c"], axis="index", copy=copy),
         lambda df, copy: df.rename_axis(index="test", copy=copy),
         lambda df, copy: df.rename_axis(columns="test", copy=copy),
@@ -84,6 +85,7 @@ def test_copy_shallow(using_copy_on_write):
         "rename",
         "reindex",
         "reindex_like",
+        "align",
         "set_axis",
         "rename_axis0",
         "rename_axis1",
@@ -115,22 +117,96 @@ def test_methods_copy_keyword(
     df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]}, index=index)
     df2 = method(df, copy=copy)
 
-    share_memory = (using_copy_on_write and copy is not True) or copy is False
+    share_memory = using_copy_on_write or copy is False
 
     if request.node.callspec.id.startswith("reindex-"):
         # TODO copy=False without CoW still returns a copy in this case
         if not using_copy_on_write and not using_array_manager and copy is False:
             share_memory = False
-        # TODO copy=True with CoW still returns a view
-        if using_copy_on_write:
-            share_memory = True
 
     if share_memory:
         assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
     else:
         assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
 
 
+@pytest.mark.parametrize("copy", [True, None, False])
+@pytest.mark.parametrize(
+    "method",
+    [
+        lambda ser, copy: ser.rename(index={0: 100}, copy=copy),
+        lambda ser, copy: ser.reindex(index=ser.index, copy=copy),
+        lambda ser, copy: ser.reindex_like(ser, copy=copy),
+        lambda ser, copy: ser.align(ser, copy=copy)[0],
+        lambda ser, copy: ser.set_axis(["a", "b", "c"], axis="index", copy=copy),
+        lambda ser, copy: ser.rename_axis(index="test", copy=copy),
+        lambda ser, copy: ser.astype("int64", copy=copy),
+        lambda ser, copy: ser.swaplevel(0, 1, copy=copy),
+        lambda ser, copy: ser.swapaxes(0, 0, copy=copy),
+        lambda ser, copy: ser.truncate(0, 5, copy=copy),
+        lambda ser, copy: ser.infer_objects(copy=copy),
+        lambda ser, copy: ser.to_timestamp(copy=copy),
+        lambda ser, copy: ser.to_period(freq="D", copy=copy),
+        lambda ser, copy: ser.tz_localize("US/Central", copy=copy),
+        lambda ser, copy: ser.tz_convert("US/Central", copy=copy),
+        lambda ser, copy: ser.set_flags(allows_duplicate_labels=False, copy=copy),
+    ],
+    ids=[
+        "rename",
+        "reindex",
+        "reindex_like",
+        "align",
+        "set_axis",
+        "rename_axis0",
+        "astype",
+        "swaplevel",
+        "swapaxes",
+        "truncate",
+        "infer_objects",
+        "to_timestamp",
+        "to_period",
+        "tz_localize",
+        "tz_convert",
+        "set_flags",
+    ],
+)
+def test_methods_series_copy_keyword(request, method, copy, using_copy_on_write):
+    index = None
+    if "to_timestamp" in request.node.callspec.id:
+        index = period_range("2012-01-01", freq="D", periods=3)
+    elif "to_period" in request.node.callspec.id:
+        index = date_range("2012-01-01", freq="D", periods=3)
+    elif "tz_localize" in request.node.callspec.id:
+        index = date_range("2012-01-01", freq="D", periods=3)
+    elif "tz_convert" in request.node.callspec.id:
+        index = date_range("2012-01-01", freq="D", periods=3, tz="Europe/Brussels")
+    elif "swaplevel" in request.node.callspec.id:
+        index = MultiIndex.from_arrays([[1, 2, 3], [4, 5, 6]])
+
+    ser = Series([1, 2, 3], index=index)
+    ser2 = method(ser, copy=copy)
+
+    share_memory = using_copy_on_write or copy is False
+
+    if share_memory:
+        assert np.shares_memory(get_array(ser2), get_array(ser))
+    else:
+        assert not np.shares_memory(get_array(ser2), get_array(ser))
+
+
+@pytest.mark.parametrize("copy", [True, None, False])
+def test_transpose_copy_keyword(using_copy_on_write, copy, using_array_manager):
+    df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6]})
+    result = df.transpose(copy=copy)
+    share_memory = using_copy_on_write or copy is False or copy is None
+    share_memory = share_memory and not using_array_manager
+
+    if share_memory:
+        assert np.shares_memory(get_array(df, "a"), get_array(result, 0))
+    else:
+        assert not np.shares_memory(get_array(df, "a"), get_array(result, 0))
+
+
 # -----------------------------------------------------------------------------
 # DataFrame methods returning new DataFrame using shallow copy
 
@@ -1119,14 +1195,13 @@ def test_set_flags(using_copy_on_write):
         tm.assert_series_equal(ser, expected)
 
 
-@pytest.mark.parametrize("copy_kwargs", [{"copy": True}, {}])
 @pytest.mark.parametrize("kwargs", [{"mapper": "test"}, {"index": "test"}])
-def test_rename_axis(using_copy_on_write, kwargs, copy_kwargs):
+def test_rename_axis(using_copy_on_write, kwargs):
     df = DataFrame({"a": [1, 2, 3, 4]}, index=Index([1, 2, 3, 4], name="a"))
     df_orig = df.copy()
-    df2 = df.rename_axis(**kwargs, **copy_kwargs)
+    df2 = df.rename_axis(**kwargs)
 
-    if using_copy_on_write and not copy_kwargs:
+    if using_copy_on_write:
         assert np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
     else:
         assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))

pandas/tests/frame/methods/test_reindex.py

@@ -149,7 +149,10 @@ def test_reindex_copies_ea(self, using_copy_on_write):
 
         # pass both columns and index
         result2 = df.reindex(columns=cols, index=df.index, copy=True)
-        assert not np.shares_memory(result2[0].array._data, df[0].array._data)
+        if using_copy_on_write:
+            assert np.shares_memory(result2[0].array._data, df[0].array._data)
+        else:
+            assert not np.shares_memory(result2[0].array._data, df[0].array._data)
 
     @td.skip_array_manager_not_yet_implemented
     def test_reindex_date_fill_value(self):