deprecate default args as positional in set_axis

Author: MarcoGorelli

pandas/core/frame.py

@@ -77,6 +77,7 @@
     Appender,
     Substitution,
     deprecate_kwarg,
+    deprecate_nonkeyword_arguments,
     doc,
     rewrite_axis_style_signature,
 )
@@ -4675,6 +4676,7 @@ def set_axis(
     ) -> DataFrame | None:
         ...
 
+    @deprecate_nonkeyword_arguments(version="2.0", allowed_args=["self", "labels"])
     @Appender(
         """
         Examples

pandas/core/generic.py

@@ -9409,7 +9409,7 @@ def shift(
         else:
             new_ax = index.shift(periods, freq)
 
-        result = self.set_axis(new_ax, axis)
+        result = self.set_axis(new_ax, axis=axis)
         return result.__finalize__(self, method="shift")
 
     @final

pandas/core/series.py

@@ -51,6 +51,7 @@
 from pandas.util._decorators import (
     Appender,
     Substitution,
+    deprecate_nonkeyword_arguments,
     doc,
 )
 from pandas.util._validators import (
@@ -4446,6 +4447,7 @@ def set_axis(self, labels, *, inplace: Literal[True]) -> None:
     def set_axis(self, labels, axis: Axis = ..., inplace: bool = ...) -> Series | None:
         ...
 
+    @deprecate_nonkeyword_arguments(version="2.0", allowed_args=["self", "labels"])
     @Appender(
         """
         Examples

pandas/tests/frame/methods/test_set_axis.py

@@ -98,3 +98,14 @@ class TestSeriesSetAxis(SharedSetAxisTests):
     def obj(self):
         ser = Series(np.arange(4), index=[1, 3, 5, 7], dtype="int64")
         return ser
+
+
+def test_nonkeyword_arguments_deprecation_warning():
+    # https://github.com/pandas-dev/pandas/issues/41485
+    df = DataFrame({"a": [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):
+        df.set_axis([1, 2, 4], False)

pandas/tests/reshape/concat/test_categorical.py

@@ -148,8 +148,8 @@ def test_categorical_index_preserver(self):
         result = pd.concat([df2, df3])
         expected = pd.concat(
             [
-                df2.set_axis(df2.index.astype(object), 0),
-                df3.set_axis(df3.index.astype(object), 0),
+                df2.set_axis(df2.index.astype(object), axis=0),
+                df3.set_axis(df3.index.astype(object), axis=0),
             ]
         )
         tm.assert_frame_equal(result, expected)