Deprecate passing default arguments as positional in reset_index (#41496)

Author: MarcoGorelli

doc/source/whatsnew/v1.3.0.rst

@@ -684,6 +684,7 @@ Deprecations
 - Deprecated passing arguments as positional in :meth:`DataFrame.sort_index` and :meth:`Series.sort_index` (:issue:`41485`)
 - Deprecated passing arguments as positional in :meth:`DataFrame.drop_duplicates` (except for ``subset``), :meth:`Series.drop_duplicates`, :meth:`Index.drop_duplicates` and :meth:`MultiIndex.drop_duplicates`(:issue:`41485`)
 - Deprecated passing arguments (apart from ``value``) as positional in :meth:`DataFrame.fillna` and :meth:`Series.fillna` (:issue:`41485`)
+- Deprecated passing arguments as positional in :meth:`DataFrame.reset_index` (other than ``"level"``) and :meth:`Series.reset_index` (:issue:`41485`)
 - Deprecated construction of :class:`Series` or :class:`DataFrame` with ``DatetimeTZDtype`` data and ``datetime64[ns]`` dtype.  Use ``Series(data).dt.tz_localize(None)`` instead (:issue:`41555`,:issue:`33401`)
 - Deprecated passing arguments as positional in :meth:`DataFrame.where` and :meth:`Series.where` (other than ``"cond"`` and ``"other"``) (:issue:`41485`)
 

pandas/core/frame.py

@@ -5596,6 +5596,7 @@ def reset_index(
     ) -> DataFrame | None:
         ...
 
+    @deprecate_nonkeyword_arguments(version=None, allowed_args=["self", "level"])
     def reset_index(
         self,
         level: Hashable | Sequence[Hashable] | None = None,

pandas/core/series.py

@@ -1308,6 +1308,7 @@ def repeat(self, repeats, axis=None) -> Series:
             self, method="repeat"
         )
 
+    @deprecate_nonkeyword_arguments(version=None, allowed_args=["self", "level"])
     def reset_index(self, level=None, drop=False, name=None, inplace=False):
         """
         Generate a new DataFrame or Series with the index reset.

pandas/tests/frame/methods/test_reset_index.py

@@ -671,3 +671,16 @@ def test_reset_index_multiindex_nat():
         index=pd.DatetimeIndex(["2015-07-01", "2015-07-02", "NaT"], name="tstamp"),
     )
     tm.assert_frame_equal(result, expected)
+
+
+def test_drop_pos_args_deprecation():
+    # https://github.com/pandas-dev/pandas/issues/41485
+    df = DataFrame({"a": [1, 2, 3]}).set_index("a")
+    msg = (
+        r"In a future version of pandas all arguments of DataFrame\.reset_index "
+        r"except for the argument 'level' will be keyword-only"
+    )
+    with tm.assert_produces_warning(FutureWarning, match=msg):
+        result = df.reset_index("a", False)
+    expected = DataFrame({"a": [1, 2, 3]})
+    tm.assert_frame_equal(result, expected)

pandas/tests/series/methods/test_reset_index.py

@@ -148,6 +148,18 @@ def test_reset_index_with_drop(self, series_with_multilevel_index):
         assert isinstance(deleveled, Series)
         assert deleveled.index.name == ser.index.name
 
+    def test_drop_pos_args_deprecation(self):
+        # https://github.com/pandas-dev/pandas/issues/41485
+        ser = Series([1, 2, 3], index=Index([1, 2, 3], name="a"))
+        msg = (
+            r"In a future version of pandas all arguments of Series\.reset_index "
+            r"except for the argument 'level' will be keyword-only"
+        )
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            result = ser.reset_index("a", False)
+        expected = DataFrame({"a": [1, 2, 3], 0: [1, 2, 3]})
+        tm.assert_frame_equal(result, expected)
+
 
 @pytest.mark.parametrize(
     "array, dtype",