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CoW - don't try to update underlying values of Series/column inplace for inplace operator #55745

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merged 3 commits into from
Nov 17, 2023
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CoW - don't try to update underlying values of Series/column inplace for inplace operator #55745

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34eee1e
CoW - don't try to update underlying values of Series/column inplace …
jorisvandenbossche Oct 28, 2023
4e499cb
Merge remote-tracking branch 'upstream/main' into cow-column-inplace-op
jorisvandenbossche Nov 17, 2023
bfb0ad0
add gh ref
jorisvandenbossche Nov 17, 2023
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7 changes: 6 additions & 1 deletion pandas/core/generic.py
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Original file line number Diff line number Diff line change
Expand Up @@ -12398,7 +12398,12 @@ def _inplace_method(self, other, op) -> Self:

result = op(self, other)

if self.ndim == 1 and result._indexed_same(self) and result.dtype == self.dtype:
if (
self.ndim == 1
and result._indexed_same(self)
and result.dtype == self.dtype
and not using_copy_on_write()
):
# GH#36498 this inplace op can _actually_ be inplace.
# Item "ArrayManager" of "Union[ArrayManager, SingleArrayManager,
# BlockManager, SingleBlockManager]" has no attribute "setitem_inplace"
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16 changes: 13 additions & 3 deletions pandas/tests/copy_view/test_methods.py
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Expand Up @@ -1806,12 +1806,22 @@ def test_update_chained_assignment(using_copy_on_write):
tm.assert_frame_equal(df, df_orig)


def test_inplace_arithmetic_series():
def test_inplace_arithmetic_series(using_copy_on_write):
ser = Series([1, 2, 3])
ser_orig = ser.copy()
data = get_array(ser)
ser *= 2
assert np.shares_memory(get_array(ser), data)
tm.assert_numpy_array_equal(data, get_array(ser))
if using_copy_on_write:
# https://github.com/pandas-dev/pandas/pull/55745
# changed to NOT update inplace because there is no benefit (actual
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GH ref pointing back to this PR/discussion

# operation already done non-inplace). This was only for the optics
# of updating the backing array inplace, but we no longer want to make
# that guarantee
assert not np.shares_memory(get_array(ser), data)
tm.assert_numpy_array_equal(data, get_array(ser_orig))
else:
assert np.shares_memory(get_array(ser), data)
tm.assert_numpy_array_equal(data, get_array(ser))


def test_inplace_arithmetic_series_with_reference(
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