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Jan 5, 2023
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TST: Add test for CoW in pop #50569

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21 changes: 21 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 @@ -174,6 +174,27 @@ def test_select_dtypes(using_copy_on_write):
tm.assert_frame_equal(df, df_orig)


def test_pop(using_copy_on_write):
df = DataFrame({"a": [1, 2, 3], "b": [4, 5, 6], "c": [0.1, 0.2, 0.3]})
df_orig = df.copy()
view_original = df[:]
result = df.pop("a")

assert np.shares_memory(result.values, get_array(view_original, "a"))
assert np.shares_memory(get_array(df, "b"), get_array(view_original, "b"))

if using_copy_on_write:
result.iloc[0] = 0
assert not np.shares_memory(result.values, get_array(view_original, "a"))
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Suggested change
assert not np.shares_memory(result.values, get_array(view_original, "a"))
assert not np.shares_memory(result.values, get_array(view_original, "a"))
assert df.iloc[0, 0] == 1

To ensure the original wasn't modified?

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Ah, no, nevermind. pop of course removed that column from df, so we don't have to check it there, and that's the wholeponit of having this view_original (which is already checked below that it is still equal to the original dataframe)

df.iloc[0, 0] = 0
if using_copy_on_write:
assert not np.shares_memory(get_array(df, "b"), get_array(view_original, "b"))
tm.assert_frame_equal(view_original, df_orig)
else:
expected = DataFrame({"a": [1, 2, 3], "b": [0, 5, 6], "c": [0.1, 0.2, 0.3]})
tm.assert_frame_equal(view_original, expected)


@pytest.mark.parametrize(
"func",
[
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