DEPR: Enforce deprecation of removing axis from all groupby ops (#57109)

* DEPR: Enforce deprecation of removing axis from all groupby ops

* Add note on fillna and cleanup

* Doc fixups

* Remove corrwith axis=1 test

* Remove corrwith axis=1 test

* Skip corrwith docstring validation

Author: rhshadrach

ci/code_checks.sh

@@ -179,6 +179,7 @@ if [[ -z "$CHECK" || "$CHECK" == "docstrings" ]]; then
         pandas.core.groupby.SeriesGroupBy.rolling\
         pandas.core.groupby.DataFrameGroupBy.hist\
         pandas.core.groupby.DataFrameGroupBy.plot\
+        pandas.core.groupby.DataFrameGroupBy.corrwith\
         pandas.core.groupby.SeriesGroupBy.plot\
         pandas.core.window.rolling.Rolling.quantile\
         pandas.core.window.expanding.Expanding.quantile # There should be no backslash in the final line, please keep this comment in the last ignored function

doc/source/reference/groupby.rst

@@ -80,7 +80,6 @@ Function application
    DataFrameGroupBy.describe
    DataFrameGroupBy.diff
    DataFrameGroupBy.ffill
-   DataFrameGroupBy.fillna
    DataFrameGroupBy.first
    DataFrameGroupBy.head
    DataFrameGroupBy.idxmax
@@ -131,7 +130,6 @@ Function application
    SeriesGroupBy.describe
    SeriesGroupBy.diff
    SeriesGroupBy.ffill
-   SeriesGroupBy.fillna
    SeriesGroupBy.first
    SeriesGroupBy.head
    SeriesGroupBy.last

doc/source/user_guide/groupby.rst

@@ -289,7 +289,7 @@ the number of groups, which is the same as the length of the ``groups`` dictiona
    In [1]: gb.<TAB>  # noqa: E225, E999
    gb.agg        gb.boxplot    gb.cummin     gb.describe   gb.filter     gb.get_group  gb.height     gb.last       gb.median     gb.ngroups    gb.plot       gb.rank       gb.std        gb.transform
    gb.aggregate  gb.count      gb.cumprod    gb.dtype      gb.first      gb.groups     gb.hist       gb.max        gb.min        gb.nth        gb.prod       gb.resample   gb.sum        gb.var
-   gb.apply      gb.cummax     gb.cumsum     gb.fillna     gb.gender     gb.head       gb.indices    gb.mean       gb.name       gb.ohlc       gb.quantile   gb.size       gb.tail       gb.weight
+   gb.apply      gb.cummax     gb.cumsum     gb.gender     gb.head       gb.indices    gb.mean       gb.name       gb.ohlc       gb.quantile   gb.size       gb.tail       gb.weight
 
 .. _groupby.multiindex:
 

doc/source/whatsnew/v3.0.0.rst

@@ -101,6 +101,8 @@ Deprecations
 
 Removal of prior version deprecations/changes
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+- Removed :meth:`DataFrameGroupby.fillna` and :meth:`SeriesGroupBy.fillna` (:issue:`55719`)
+- Removed ``axis`` argument from all groupby operations (:issue:`50405`)
 - Removed deprecated argument ``obj`` in :meth:`.DataFrameGroupBy.get_group` and :meth:`.SeriesGroupBy.get_group` (:issue:`53545`)
 
 .. ---------------------------------------------------------------------------

pandas/core/groupby/base.py

@@ -70,7 +70,6 @@ class OutputKey:
         "cumsum",
         "diff",
         "ffill",
-        "fillna",
         "ngroup",
         "pct_change",
         "rank",