ENH: Deprecate non-keyword arguments for Index.set_names.

doc/source/whatsnew/v1.3.0.rst

@@ -674,6 +674,7 @@ 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 as positional in :meth:`Index.set_names` (except for ``names``) (:issue:`41485`)
 - Deprecated special treatment of lists with first element a Categorical in the :class:`DataFrame` constructor; pass as ``pd.DataFrame({col: categorical, ...})`` instead (:issue:`38845`)
 - Deprecated passing arguments as positional (except for ``"method"``) in :meth:`DataFrame.interpolate` and :meth:`Series.interpolate` (:issue:`41485`)
 - Deprecated passing arguments (apart from ``value``) as positional in :meth:`DataFrame.fillna` and :meth:`Series.fillna` (:issue:`41485`)

pandas/core/indexes/base.py

@@ -54,6 +54,7 @@
 from pandas.util._decorators import (
     Appender,
     cache_readonly,
+    deprecate_nonkeyword_arguments,
     doc,
 )
 
@@ -1529,6 +1530,7 @@ def _set_names(self, values, level=None) -> None:
 
     names = property(fset=_set_names, fget=_get_names)
 
+    @deprecate_nonkeyword_arguments(version=None, allowed_args=["self", "names"])
     @final
     def set_names(self, names, level=None, inplace: bool = False):
         """

pandas/tests/indexes/multi/test_get_set.py

@@ -345,6 +345,27 @@ def test_set_names_with_nlevel_1(inplace):
     tm.assert_index_equal(result, expected)
 
 
+def test_multi_set_names_pos_args_deprecation():
+    # GH#41485
+    idx = MultiIndex.from_product([["python", "cobra"], [2018, 2019]])
+
+    msg = (
+        "In a future version of pandas all arguments of Index.set_names "
+        "except for the argument 'names' will be keyword-only"
+    )
+
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = idx.set_names(["kind", "year"], None)
+
+    expected = MultiIndex(
+        levels=[["python", "cobra"], [2018, 2019]],
+        codes=[[0, 0, 1, 1], [0, 1, 0, 1]],
+        names=["kind", "year"],
+    )
+
+    tm.assert_index_equal(result, expected)
+
+
 @pytest.mark.parametrize("ordered", [True, False])
 def test_set_levels_categorical(ordered):
     # GH13854

pandas/tests/indexes/test_base.py

@@ -1738,3 +1738,20 @@ def test_construct_from_memoryview(klass, extra_kwargs):
     result = klass(memoryview(np.arange(2000, 2005)), **extra_kwargs)
     expected = klass(range(2000, 2005), **extra_kwargs)
     tm.assert_index_equal(result, expected)
+
+
+def test_index_set_names_pos_args_deprecation():
+    # GH#41485
+    idx = Index([1, 2, 3, 4])
+
+    msg = (
+        "In a future version of pandas all arguments of Index.set_names "
+        "except for the argument 'names' will be keyword-only"
+    )
+
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = idx.set_names("quarter", None)
+
+    expected = Index([1, 2, 3, 4], name="quarter")
+
+    tm.assert_index_equal(result, expected)