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ENH/TST: expand copy-on-write to assign() method #50010

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Dec 2, 2022
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ENH/TST: expand copy-on-write to assign() method #50010

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2 changes: 1 addition & 1 deletion pandas/core/frame.py
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Original file line number Diff line number Diff line change
Expand Up @@ -4887,7 +4887,7 @@ def assign(self, **kwargs) -> DataFrame:
Portland 17.0 62.6 290.15
Berkeley 25.0 77.0 298.15
"""
data = self.copy()
data = self.copy(deep=None)

for k, v in kwargs.items():
data[k] = com.apply_if_callable(v, data)
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18 changes: 18 additions & 0 deletions pandas/tests/copy_view/test_methods.py
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Expand Up @@ -280,3 +280,21 @@ def test_head_tail(method, using_copy_on_write):
# without CoW enabled, head and tail return views. Mutating df2 also mutates df.
df2.iloc[0, 0] = 1
tm.assert_frame_equal(df, df_orig)


def test_assign(using_copy_on_write):
df = DataFrame({"a": [1, 2, 3]})
df_orig = df.copy()
df2 = df.assign()
df2._mgr._verify_integrity()
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Suggested change
df2._mgr._verify_integrity()

For future tests, you can leave out this part (I don't think it is needed to repeat in every test)

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Noted, will do.


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"))

# modify df2 to trigger CoW for that block
df2.iloc[0, 0] = 0
if using_copy_on_write:
assert not np.shares_memory(get_array(df2, "a"), get_array(df, "a"))
tm.assert_frame_equal(df, df_orig)