deprecate default args as positional in set_axis

Author: MarcoGorelli

doc/source/whatsnew/v1.3.0.rst

@@ -647,6 +647,7 @@ Deprecations
 - Deprecated setting :attr:`Categorical._codes`, create a new :class:`Categorical` with the desired codes instead (:issue:`40606`)
 - Deprecated behavior of :meth:`DatetimeIndex.union` with mixed timezones; in a future version both will be cast to UTC instead of object dtype (:issue:`39328`)
 - Deprecated using ``usecols`` with out of bounds indices for ``read_csv`` with ``engine="c"`` (:issue:`25623`)
+- Deprecated passing arguments (apart from ``labels``) as positional in :meth:`DataFrame.set_axis` and :meth:`Series.set_axis` (:issue:`41485`)
 
 .. ---------------------------------------------------------------------------
 

pandas/tests/frame/methods/test_set_axis.py

@@ -109,3 +109,11 @@ def test_nonkeyword_arguments_deprecation_warning():
     )
     with tm.assert_produces_warning(FutureWarning, match=msg):
         df.set_axis([1, 2, 4], False)
+
+    ser = Series([1, 2, 3])
+    msg = (
+        r"Starting with Pandas version 2\.0 all arguments of set_axis except for the "
+        r"arguments 'self' and 'labels' will be keyword-only"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        ser.set_axis([1, 2, 4], False)