[Pandas-dev] PDEP-8: In-place methods in pandas (i.e. deprecating the inplace keyword)

[Joris Van den Bossche]

Hi list,

There is proposal to deprecate and eventually remove the `inplace` keyword
(in most places): PDEP-8 (https://github.com/pandas-dev/pandas/pull/51466).
This has been open for quite a while, and I just updated the text to
reflect the latest state of the discussion, and wanted to bring this up on
the mailing list here as well.

Feedback goes to the PR: https://github.com/pandas-dev/pandas/pull/51466
If you want to see a rendered version of the text:
https://jorisvandenbossche.github.io/pandas-website-preview/pdeps/0008-inplace-methods-in-pandas.html
(our website does not yet render them before being merged)

And posting the abstract here as well. The PDEP proposes:

   -

   The inplace parameter will be removed from any method which can never
   update the underlying values of a pandas object inplace or which alters the
   shape of the object, and where the inplace=True option is only syntactic
   sugar for reassigning the result to the calling DataFrame/Series.
   -

   As a consequence, the inplace parameter is only kept for those methods
   that can modify the underlying values of a pandas object inplace, such as
   fillna or replace.
   -

   With the introduction of Copy-on-Write (PDEP-7[1]
   <https://jorisvandenbossche.github.io/pandas-website-preview/pdeps/0008-inplace-methods-in-pandas.html#id9>),
   users don’t need the inplace keyword to avoid a copy of the data.
   -

   For those methods that will keep the inplace=True option:
   -

      the method will do an attempt to do the operation inplace but still
      silently copy when needed (for Copy-on-Write), i.e. there is no guarantee
      it is actually done inplace.
      -

      the method will return the calling object (self), instead of the
      current None.


For the full proposal and motivation, see the links above.

Feedback welcome!
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