CLN: Misc pre-COW stuff

pandas/_testing/__init__.py

@@ -72,7 +72,6 @@
     get_obj,
 )
 from pandas._testing.contexts import (
-    assert_cow_warning,
     decompress_file,
     ensure_clean,
     raises_chained_assignment_error,
@@ -583,7 +582,6 @@ def shares_memory(left, right) -> bool:
     "assert_series_equal",
     "assert_sp_array_equal",
     "assert_timedelta_array_equal",
-    "assert_cow_warning",
     "at",
     "BOOL_DTYPES",
     "box_expected",

pandas/_testing/contexts.py

@@ -228,29 +228,3 @@ def raises_chained_assignment_error(warn=True, extra_warnings=(), extra_match=()
             warning,
             match="|".join((match, *extra_match)),
         )
-
-
-def assert_cow_warning(warn=True, match=None, **kwargs):
-    """
-    Assert that a warning is raised in the CoW warning mode.
-
-    Parameters
-    ----------
-    warn : bool, default True
-        By default, check that a warning is raised. Can be turned off by passing False.
-    match : str
-        The warning message to match against, if different from the default.
-    kwargs
-        Passed through to assert_produces_warning
-    """
-    from pandas._testing import assert_produces_warning
-
-    if not warn:
-        from contextlib import nullcontext
-
-        return nullcontext()
-
-    if not match:
-        match = "Setting a value on a view"
-
-    return assert_produces_warning(FutureWarning, match=match, **kwargs)

pandas/core/arrays/arrow/array.py

@@ -1050,8 +1050,7 @@ def _pad_or_backfill(
         copy: bool = True,
     ) -> Self:
         if not self._hasna:
-            # TODO(CoW): Not necessary anymore when CoW is the default
-            return self.copy()
+            return self
 
         if limit is None and limit_area is None:
             method = missing.clean_fill_method(method)
@@ -1084,8 +1083,7 @@ def fillna(
         value, method = validate_fillna_kwargs(value, method)
 
         if not self._hasna:
-            # TODO(CoW): Not necessary anymore when CoW is the default
-            return self.copy()
+            return self
 
         if limit is not None:
             return super().fillna(value=value, method=method, limit=limit, copy=copy)

pandas/core/internals/blocks.py

@@ -131,29 +131,6 @@
 _dtype_obj = np.dtype("object")
 
 
-COW_WARNING_GENERAL_MSG = """\
-Setting a value on a view: behaviour will change in pandas 3.0.
-You are mutating a Series or DataFrame object, and currently this mutation will
-also have effect on other Series or DataFrame objects that share data with this
-object. In pandas 3.0 (with Copy-on-Write), updating one Series or DataFrame object
-will never modify another.
-"""
-
-
-COW_WARNING_SETITEM_MSG = """\
-Setting a value on a view: behaviour will change in pandas 3.0.
-Currently, the mutation will also have effect on the object that shares data
-with this object. For example, when setting a value in a Series that was
-extracted from a column of a DataFrame, that DataFrame will also be updated:
-
-    ser = df["col"]
-    ser[0] = 0     <--- in pandas 2, this also updates `df`
-
-In pandas 3.0 (with Copy-on-Write), updating one Series/DataFrame will never
-modify another, and thus in the example above, `df` will not be changed.
-"""
-
-
 def maybe_split(meth: F) -> F:
     """
     If we have a multi-column block, split and operate block-wise.  Otherwise

pandas/errors/cow.py

@@ -22,33 +22,3 @@
     "using 'df.method({col: value}, inplace=True)' instead, to perform "
     "the operation inplace on the original object.\n\n"
 )
-
-
-_chained_assignment_warning_msg = (
-    "ChainedAssignmentError: behaviour will change in pandas 3.0!\n"
-    "You are setting values through chained assignment. Currently this works "
-    "in certain cases, but when using Copy-on-Write (which will become the "
-    "default behaviour in pandas 3.0) this will never work to update the "
-    "original DataFrame or Series, because the intermediate object on which "
-    "we are setting values will behave as a copy.\n"
-    "A typical example is when you are setting values in a column of a "
-    "DataFrame, like:\n\n"
-    'df["col"][row_indexer] = value\n\n'
-    'Use `df.loc[row_indexer, "col"] = values` instead, to perform the '
-    "assignment in a single step and ensure this keeps updating the original `df`.\n\n"
-    "See the caveats in the documentation: "
-    "https://pandas.pydata.org/pandas-docs/stable/user_guide/"
-    "indexing.html#returning-a-view-versus-a-copy\n"
-)
-
-_chained_assignment_warning_method_msg = (
-    "A value is trying to be set on a copy of a DataFrame or Series "
-    "through chained assignment using an inplace method.\n"
-    "The behavior will change in pandas 3.0. This inplace method will "
-    "never work because the intermediate object on which we are setting "
-    "values always behaves as a copy.\n\n"
-    "For example, when doing 'df[col].method(value, inplace=True)', try "
-    "using 'df.method({col: value}, inplace=True)' or "
-    "df[col] = df[col].method(value) instead, to perform "
-    "the operation inplace on the original object.\n\n"
-)

pandas/tests/copy_view/test_chained_assignment_deprecation.py

@@ -7,7 +7,6 @@
 import pandas._testing as tm
 
 
-# TODO(CoW-warn) expand the cases
 @pytest.mark.parametrize(
     "indexer", [0, [0, 1], slice(0, 2), np.array([True, False, True])]
 )

pandas/tests/copy_view/test_core_functionalities.py

@@ -46,7 +46,7 @@ def test_setitem_with_view_invalidated_does_not_copy(request):
     df["b"] = 100
     arr = get_array(df, "a")
     view = None  # noqa: F841
-    # TODO(CoW-warn) false positive? -> block gets split because of `df["b"] = 100`
+    # TODO(CoW) block gets split because of `df["b"] = 100`
     # which introduces additional refs, even when those of `view` go out of scopes
     df.iloc[0, 0] = 100
     # Setitem split the block. Since the old block shared data with view

pandas/tests/extension/json/test_json.py

@@ -218,7 +218,7 @@ def test_fillna_copy_frame(self, data_missing):
         super().test_fillna_copy_frame(data_missing)
 
     @pytest.mark.xfail(reason="Fails with CoW")
-    def test_equals_same_data_different_object(self, data, request):
+    def test_equals_same_data_different_object(self, data):
         super().test_equals_same_data_different_object(data)
 
     @pytest.mark.xfail(reason="failing on np.array(self, dtype=str)")

pandas/tests/frame/indexing/test_indexing.py

@@ -321,7 +321,6 @@ def test_setitem(self, float_frame, using_infer_string):
         # so raise/warn
         smaller = float_frame[:2]
 
-        # With CoW, adding a new column doesn't raise a warning
         smaller["col10"] = ["1", "2"]
 
         if using_infer_string:

pandas/tests/indexing/multiindex/test_setitem.py

@@ -207,8 +207,6 @@ def test_multiindex_assignment_single_dtype(self):
         )
 
         # arr can be losslessly cast to int, so this setitem is inplace
-        # INFO(CoW-warn) this does not warn because we directly took .values
-        # above, so no reference to a pandas object is alive for `view`
         df.loc[4, "c"] = arr
         exp = Series(arr, index=[8, 10], name="c", dtype="int64")
         result = df.loc[4, "c"]

pandas/tests/indexing/test_chaining_and_caching.py

@@ -324,7 +324,6 @@ def test_detect_chained_assignment_warning_stacklevel(self, rhs):
         df = DataFrame(np.arange(25).reshape(5, 5))
         df_original = df.copy()
         chained = df.loc[:3]
-        # INFO(CoW) no warning, and original dataframe not changed
         chained[2] = rhs
         tm.assert_frame_equal(df, df_original)
 

scripts/validate_unwanted_patterns.py

@@ -49,9 +49,6 @@
     "_global_config",
     "_chained_assignment_msg",
     "_chained_assignment_method_msg",
-    "_chained_assignment_warning_msg",
-    "_chained_assignment_warning_method_msg",
-    "_check_cacher",
     "_version_meson",
     # The numba extensions need this to mock the iloc object
     "_iLocIndexer",