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DOC: update Series() docstring about copy behaviour #63341

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DOC: update Series() docstring about copy behaviour #63341

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DOC: update Series() docstring about copy behaviour
jorisvandenbossche Dec 12, 2025
ee645f0
rephrase
jorisvandenbossche Dec 12, 2025
17389bf
Update pandas/core/series.py
jorisvandenbossche Dec 14, 2025
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Merge remote-tracking branch 'upstream/main' into cow-doc-series-copy
jorisvandenbossche Dec 14, 2025
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9 changes: 7 additions & 2 deletions pandas/core/series.py
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Expand Up @@ -265,8 +265,13 @@ class Series(base.IndexOpsMixin, NDFrame): # type: ignore[misc]
See the :ref:`user guide <basics.dtypes>` for more usages.
name : Hashable, default None
The name to give to the Series.
copy : bool, default False
Copy input data. Only affects Series or 1d ndarray input. See examples.
copy : bool, default None
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@jorisvandenbossche jorisvandenbossche Dec 12, 2025 •
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Related to #63144, the question is what to put here in the docstring ..

copy=None is closest to what is in the signature, but is not really meaningful by itself. Of course, the behaviour also depends on the intput, so writing that it defaults to either True or False will also be misleading for some cases.
(eg the current default False in the docstring above is not correct for array input)

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@rhshadrach rhshadrach Dec 12, 2025

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I'm fine with None here, I think the behavior is too complex to give a meaningful description in the space allowed.

Whether to copy input data. Only affects array or Series/Index input,
because for other input (e.g. a list) a new array is created anyway.
By default, will copy if the input data is a numpy or pandas array.
For Series/Index input, a shallow copy of the data is made by default.
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@rhshadrach rhshadrach Dec 12, 2025 •
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It's not quite clear to me what happens if you set it to False in the Series/Index case.

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@jorisvandenbossche jorisvandenbossche Dec 14, 2025

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It is the same as None, meaning a shallow copy (i.e. not copying right now, but still using CoW, so it is not that copy=False kind if disables CoW for this construction)

(added an explicit test for that in #63342)

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@jorisvandenbossche jorisvandenbossche Dec 14, 2025

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I was thinking to add something like:

Set to False to avoid copying array input ...
Set to True to force copying Series/Index input up front.

Would that be useful?

And then for the copy=False case for Series/Index input, I could also mention that when explaining the default, something like "For Series/Index input, a shallow copy of the data is made by default (same as copy=False)" (added the part between brackets)

That might make it clearer that essentially the default of copy=None is translated into copy=True for array input and copy=False for Series/Index input

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@rhshadrach rhshadrach Dec 14, 2025

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It's not quite clear to me what happens if you set it to False in the Series/Index case.

Ah, I had meant True (the non-default).

It is hard to evaluate without seeing the whole docstring. I'd think of starting with something like this:

Whether to copy input data, only relevant for array, Series, and Index inputs. Defaults to True on array input and False on Index/Series. Even when False on Index/Series, a shallow copy of the data is made.

Set to False to avoid copying array input at your own risk (if you
know the input data won't be modified elsewhere).

See Also
--------
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