List of functions that support in-place modification

inplace_funcs.txt

# Reference: https://github.com/pandas-dev/pandas/issues/16529

(Series/DataFrame).drop
(Series/DataFrame).drop_duplicates
(Series/DataFrame).dropna
DataFrame.set_index (with drop=False wouldn't change the data, but that doesn't seem the main use case)
DataFrame.query
DataFrame.eval


(Series/DataFrame).sort_values
(Series/DataFrame).sort_index

(Series/DataFrame).clip
(Series/DataFrame).where
(Series/DataFrame).{fillna, ffill, bfill}
(Series/DataFrame).rename_axis
(Series/DataFrame).reset_index
(Series/DataFrame).replace
(Series/DataFrame).set_axis
(Series/DataFrame).mask
(Series/DataFrame).interpolate
DataFrame.rename
Index.rename
Index.set_names
MultiIndex.set_levels
MultiIndex.set_labels
pandas.core.resample.Resampler.interpolate

pandas.eval (with inplace=False the value is not returned but set to an argument target)

(Series/DataFrame/Panel).clip_lower
(Series/DataFrame/Panel).clip_upper
pandas.Panel.clip
pandas.Panel.drop
pandas.Panel.dropna
pandas.Panel.sort_index