allow level to be passed positionally

Author: MarcoGorelli

doc/source/user_guide/cookbook.rst

@@ -312,7 +312,7 @@ The :ref:`multindexing <advanced.hierarchical>` docs.
    df.columns = pd.MultiIndex.from_tuples([tuple(c.split("_")) for c in df.columns])
    df
    # Now stack & Reset
-   df = df.stack(0).reset_index(level=1)
+   df = df.stack(0).reset_index(1)
    df
    # And fix the labels (Notice the label 'level_1' got added automatically)
    df.columns = ["Sample", "All_X", "All_Y"]

doc/source/whatsnew/v1.3.0.rst

@@ -647,7 +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 as positional in :meth:`DataFrame.reset_index` and :meth:`Series.reset_index` (:issue:`41485`)
+- Deprecated passing arguments as positional (except for ``"level"``) in :meth:`DataFrame.reset_index` and :meth:`Series.reset_index` (:issue:`41485`)
 
 .. ---------------------------------------------------------------------------
 

pandas/core/frame.py

@@ -5568,7 +5568,7 @@ def reset_index(
     ) -> DataFrame | None:
         ...
 
-    @deprecate_nonkeyword_arguments(version="2.0", allowed_args=["self"])
+    @deprecate_nonkeyword_arguments(version="2.0", allowed_args=["self", "level"])
     def reset_index(
         self,
         level: Hashable | Sequence[Hashable] | None = None,

pandas/core/generic.py

@@ -1847,7 +1847,7 @@ def _drop_labels_or_levels(self, keys, axis: int = 0):
         if axis == 0:
             # Handle dropping index levels
             if levels_to_drop:
-                dropped.reset_index(level=levels_to_drop, drop=True, inplace=True)
+                dropped.reset_index(levels_to_drop, drop=True, inplace=True)
 
             # Handle dropping columns labels
             if labels_to_drop:

pandas/core/series.py

@@ -1276,7 +1276,7 @@ def repeat(self, repeats, axis=None) -> Series:
             self, method="repeat"
         )
 
-    @deprecate_nonkeyword_arguments(version="2.0", allowed_args=["self"])
+    @deprecate_nonkeyword_arguments(version="2.0", 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_droplevel.py

@@ -20,7 +20,7 @@ def test_droplevel(self, frame_or_series):
             df = df.iloc[:, 0]
 
         # test that dropping of a level in index works
-        expected = df.reset_index(level="a", drop=True)
+        expected = df.reset_index("a", drop=True)
         result = df.droplevel("a", axis="index")
         tm.assert_equal(result, expected)
 

pandas/tests/frame/methods/test_reset_index.py

@@ -142,18 +142,18 @@ def test_reset_index(self, float_frame):
 
         # only remove certain columns
         df = float_frame.reset_index().set_index(["index", "A", "B"])
-        rs = df.reset_index(level=["A", "B"])
+        rs = df.reset_index(["A", "B"])
 
         # TODO should reset_index check_names ?
         tm.assert_frame_equal(rs, float_frame, check_names=False)
 
-        rs = df.reset_index(level=["index", "A", "B"])
+        rs = df.reset_index(["index", "A", "B"])
         tm.assert_frame_equal(rs, float_frame.reset_index(), check_names=False)
 
-        rs = df.reset_index(level=["index", "A", "B"])
+        rs = df.reset_index(["index", "A", "B"])
         tm.assert_frame_equal(rs, float_frame.reset_index(), check_names=False)
 
-        rs = df.reset_index(level="A")
+        rs = df.reset_index("A")
         xp = float_frame.reset_index().set_index(["index", "B"])
         tm.assert_frame_equal(rs, xp, check_names=False)
 
@@ -165,7 +165,7 @@ def test_reset_index(self, float_frame):
         tm.assert_frame_equal(df, reset, check_names=False)
 
         df = float_frame.reset_index().set_index(["index", "A", "B"])
-        rs = df.reset_index(level="A", drop=True)
+        rs = df.reset_index("A", drop=True)
         xp = float_frame.copy()
         del xp["A"]
         xp = xp.set_index(["B"], append=True)
@@ -262,23 +262,23 @@ def test_reset_index_multiindex_col(self):
             MultiIndex.from_arrays([[0, 1, 2], ["x", "y", "z"]], names=["d", "a"]),
             columns=[["b", "b", "c"], ["mean", "median", "mean"]],
         )
-        rs = df.reset_index(level="a")
+        rs = df.reset_index("a")
         xp = DataFrame(
             full,
             Index([0, 1, 2], name="d"),
             columns=[["a", "b", "b", "c"], ["", "mean", "median", "mean"]],
         )
         tm.assert_frame_equal(rs, xp)
 
-        rs = df.reset_index(level="a", col_fill=None)
+        rs = df.reset_index("a", col_fill=None)
         xp = DataFrame(
             full,
             Index(range(3), name="d"),
             columns=[["a", "b", "b", "c"], ["a", "mean", "median", "mean"]],
         )
         tm.assert_frame_equal(rs, xp)
 
-        rs = df.reset_index(level="a", col_fill="blah", col_level=1)
+        rs = df.reset_index("a", col_fill="blah", col_level=1)
         xp = DataFrame(
             full,
             Index(range(3), name="d"),
@@ -665,7 +665,7 @@ def test_reset_index_multiindex_nat():
     tstamp = date_range("2015-07-01", freq="D", periods=3)
     df = DataFrame({"id": idx, "tstamp": tstamp, "a": list("abc")})
     df.loc[2, "tstamp"] = pd.NaT
-    result = df.set_index(["id", "tstamp"]).reset_index(level="id")
+    result = df.set_index(["id", "tstamp"]).reset_index("id")
     expected = DataFrame(
         {"id": range(3), "a": list("abc")},
         index=pd.DatetimeIndex(["2015-07-01", "2015-07-02", "NaT"], name="tstamp"),
@@ -678,7 +678,7 @@ def test_drop_pos_args_deprecation():
     df = DataFrame({"a": [1, 2, 3]}).set_index("a")
     msg = (
         r"Starting with Pandas version 2\.0 all arguments of reset_index except for "
-        r"the argument 'self' will be keyword-only"
+        r"the arguments 'self' and 'level' will be keyword-only"
     )
     with tm.assert_produces_warning(FutureWarning, match=msg):
-        df.reset_index("a")
+        df.reset_index("a", False)

pandas/tests/groupby/test_grouping.py

@@ -291,7 +291,7 @@ def test_grouper_column_and_index(self):
 
         # Grouping a single-index frame by a column and the index should
         # be equivalent to resetting the index and grouping by two columns
-        df_single = df_multi.reset_index(level="outer")
+        df_single = df_multi.reset_index("outer")
         result = df_single.groupby(["B", pd.Grouper(level="inner")]).mean()
         expected = df_single.reset_index().groupby(["B", "inner"]).mean()
         tm.assert_frame_equal(result, expected)

pandas/tests/reshape/merge/test_merge_index_as_string.py

@@ -96,11 +96,11 @@ def compute_expected(df_left, df_right, on=None, left_on=None, right_on=None, ho
     # Drop index levels that aren't involved in the merge
     drop_left = [n for n in left_levels if n not in left_on]
     if drop_left:
-        df_left = df_left.reset_index(level=drop_left, drop=True)
+        df_left = df_left.reset_index(drop_left, drop=True)
 
     drop_right = [n for n in right_levels if n not in right_on]
     if drop_right:
-        df_right = df_right.reset_index(level=drop_right, drop=True)
+        df_right = df_right.reset_index(drop_right, drop=True)
 
     # Convert remaining index levels to columns
     reset_left = [n for n in left_levels if n in left_on]

pandas/tests/series/methods/test_reset_index.py

@@ -107,7 +107,7 @@ def test_reset_index_level(self):
                 s.reset_index(level=[0, 1, 2])
 
         # Check that .reset_index([],drop=True) doesn't fail
-        result = Series(range(4)).reset_index(level=[], drop=True)
+        result = Series(range(4)).reset_index([], drop=True)
         expected = Series(range(4))
         tm.assert_series_equal(result, expected)
 
@@ -127,14 +127,14 @@ def test_reset_index_drop_errors(self):
         # KeyError raised for series index when passed level name is missing
         s = Series(range(4))
         with pytest.raises(KeyError, match="does not match index name"):
-            s.reset_index(level="wrong", drop=True)
+            s.reset_index("wrong", drop=True)
         with pytest.raises(KeyError, match="does not match index name"):
-            s.reset_index(level="wrong")
+            s.reset_index("wrong")
 
         # KeyError raised for series when level to be dropped is missing
         s = Series(range(4), index=MultiIndex.from_product([[1, 2]] * 2))
         with pytest.raises(KeyError, match="not found"):
-            s.reset_index(level="wrong", drop=True)
+            s.reset_index("wrong", drop=True)
 
     def test_reset_index_with_drop(self, series_with_multilevel_index):
         ser = series_with_multilevel_index
@@ -148,6 +148,16 @@ 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"Starting with Pandas version 2\.0 all arguments of reset_index except "
+            r"for the arguments 'self' and 'level' will be keyword-only"
+        )
+        with tm.assert_produces_warning(FutureWarning, match=msg):
+            ser.reset_index("a", False)
+
 
 @pytest.mark.parametrize(
     "array, dtype",