DEPR: Deprecate passing positional arguments in {DataFrame,Series}.groupby (except by and level)

Author: MarcoGorelli

doc/source/whatsnew/v3.0.0.rst

@@ -514,6 +514,7 @@ Other Deprecations
 - Deprecated :meth:`Timestamp.utcnow`, use ``Timestamp.now("UTC")`` instead (:issue:`56680`)
 - Deprecated ``pd.core.internals.api.maybe_infer_ndim`` (:issue:`40226`)
 - Deprecated allowing non-keyword arguments in :meth:`DataFrame.all`, :meth:`DataFrame.min`, :meth:`DataFrame.max`, :meth:`DataFrame.sum`, :meth:`DataFrame.prod`, :meth:`DataFrame.mean`, :meth:`DataFrame.median`, :meth:`DataFrame.sem`, :meth:`DataFrame.var`, :meth:`DataFrame.std`, :meth:`DataFrame.skew`, :meth:`DataFrame.kurt`, :meth:`Series.all`,  :meth:`Series.min`, :meth:`Series.max`, :meth:`Series.sum`, :meth:`Series.prod`, :meth:`Series.mean`, :meth:`Series.median`, :meth:`Series.sem`, :meth:`Series.var`, :meth:`Series.std`, :meth:`Series.skew`, and :meth:`Series.kurt`. (:issue:`57087`)
+- Deprecated allowing non-keyword arguments in :meth:`DataFrame.groupby` and :meth:`Series.groupby` except ``by`` and ``level``. (:issue:`62102`)
 - Deprecated allowing non-keyword arguments in :meth:`Series.to_markdown` except ``buf``. (:issue:`57280`)
 - Deprecated allowing non-keyword arguments in :meth:`Series.to_string` except ``buf``. (:issue:`57280`)
 - Deprecated behavior of :meth:`.DataFrameGroupBy.groups` and :meth:`.SeriesGroupBy.groups`, in a future version ``groups`` by one element list will return tuple instead of scalar. (:issue:`58858`)

pandas/core/frame.py

@@ -9368,6 +9368,9 @@ def update(
         )
     )
     @Appender(_shared_docs["groupby"] % _shared_doc_kwargs)
+    @deprecate_nonkeyword_arguments(
+        Pandas4Warning, allowed_args=["self", "by", "level"], name="groupby"
+    )
     def groupby(
         self,
         by=None,

pandas/core/series.py

@@ -1966,6 +1966,9 @@ def _set_name(
         )
     )
     @Appender(_shared_docs["groupby"] % _shared_doc_kwargs)
+    @deprecate_nonkeyword_arguments(
+        Pandas4Warning, allowed_args=["self", "by", "level"], name="groupby"
+    )
     def groupby(
         self,
         by=None,