make rename compatible with parent

Author: MarcoGorelli

pandas/core/groupby/groupby.py

@@ -28,6 +28,7 @@ class providing the base-class of operations.
     Sequence,
     TypeVar,
     Union,
+    cast,
 )
 
 import numpy as np
@@ -1698,7 +1699,7 @@ def size(self) -> FrameOrSeriesUnion:
             result = self._obj_1d_constructor(result)
 
         if not self.as_index:
-            result = result.rename("size").reset_index()
+            result = cast(Series, result.rename("size")).reset_index()
 
         return self._reindex_output(result, fill_value=0)
 

pandas/core/series.py

@@ -4345,14 +4345,16 @@ def align(
 
     def rename(
         self,
-        index=None,
+        mapper=None,
         *,
+        index=None,
+        columns=None,
         axis=None,
         copy=True,
         inplace=False,
         level=None,
         errors="ignore",
-    ):
+    ) -> Series | None:
         """
         Alter Series index labels or name.
 
@@ -4368,7 +4370,7 @@ def rename(
         ----------
         axis : {0 or "index"}
             Unused. Accepted for compatibility with DataFrame method only.
-        index : scalar, hashable sequence, dict-like or function, optional
+        mapper : scalar, hashable sequence, dict-like or function, optional
             Functions or dict-like are transformations to apply to
             the index.
             Scalar or hashable sequence-like will alter the ``Series.name``
@@ -4412,12 +4414,18 @@ def rename(
         5    3
         dtype: int64
         """
-        if callable(index) or is_dict_like(index):
+        if index is not None and mapper is not None:
+            raise TypeError("Cannot specify both 'mapper' and 'index'")
+        if index is None and mapper is None:
+            raise TypeError("Must pass a mapper")
+        if mapper is None:
+            mapper = index
+        if callable(mapper) or is_dict_like(mapper):
             return super().rename(
-                index, copy=copy, inplace=inplace, level=level, errors=errors
+                mapper, copy=copy, inplace=inplace, level=level, errors=errors
             )
         else:
-            return self._set_name(index, inplace=inplace)
+            return self._set_name(mapper, inplace=inplace)
 
     @overload
     def set_axis(

pandas/tests/series/methods/test_rename.py

@@ -1,6 +1,7 @@
 from datetime import datetime
 
 import numpy as np
+import pytest
 
 from pandas import (
     Index,
@@ -101,3 +102,15 @@ def test_rename_callable(self):
         tm.assert_series_equal(result, expected)
 
         assert result.name == expected.name
+
+    def test_rename_method_and_index(self):
+        # GH 40977
+        s = Series([1, 2])
+        with pytest.raises(TypeError, match="Cannot specify both 'mapper' and 'index'"):
+            s.rename(str, index=str)
+
+    def test_rename_no_method_no_index(self):
+        # GH 40977
+        s = Series([1, 2])
+        with pytest.raises(TypeError, match="Must pass a mapper"):
+            s.rename(inplace=False)