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TST: CoW with df.isetitem() #50692

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Merged
merged 4 commits into from
Jan 12, 2023
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TST: CoW with df.isetitem() #50692

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TST: CoW with df.isetitem()
lithomas1 Jan 12, 2023
cef1087
Merge branch 'main' of https://github.com/pandas-dev/pandas into tet-…
lithomas1 Jan 12, 2023
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Address review comments
lithomas1 Jan 12, 2023
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Merge branch 'main' into test-cow-isetitem
lithomas1 Jan 12, 2023
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22 changes: 22 additions & 0 deletions pandas/tests/copy_view/test_methods.py
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Original file line number Diff line number Diff line change
Expand Up @@ -759,3 +759,25 @@ def test_squeeze(using_copy_on_write):
# Without CoW the original will be modified
assert np.shares_memory(series.values, get_array(df, "a"))
assert df.loc[0, "a"] == 0


def test_isetitem(using_copy_on_write):
df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [7, 8, 9]})
df_orig = df.copy()
df2 = df.copy(deep=None) # Trigger a CoW
df2.isetitem(1, np.array([-1, -2, -3]))

if using_copy_on_write:
assert np.shares_memory(df["c"].values, df2["c"].values)
assert np.shares_memory(df["a"].values, df2["a"].values)
else:
assert not np.shares_memory(df["c"].values, df2["c"].values)
assert not np.shares_memory(df["a"].values, df2["a"].values)

df2.loc[0, "a"] = 0
tm.assert_series_equal(df["a"], df_orig["a"]) # Original is unchanged
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Can we use get_array? A regular getitem sets up references which is what we want to avoid here

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Sorry wrong line, in the np.shares_memory and any reason why we don't compare the whole object?

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Can we use get_array? A regular getitem sets up references which is what we want to avoid here

Changed. Originally, I had put this test in test_setitem.py does the shares_memory checks like this.
Should we change that file over in the future?

Sorry wrong line, in the np.shares_memory and any reason why we don't compare the whole object?

Updated, I had this left over from testing, sorry.

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No worries.

Hm I would not change any existing tests as of right now (still early in CoW adaption). In general this is fine if CoW is not activated, but when explicitly testing CoW we should avoid setting up references to avoid side effects


if using_copy_on_write:
assert np.shares_memory(df["c"].values, df2["c"].values)
else:
assert not np.shares_memory(df["c"].values, df2["c"].values)