BUG: Series.rename raises error on values accepted by Series construc…

doc/source/whatsnew/v0.25.1.rst

@@ -155,7 +155,7 @@ ExtensionArray
 Other
 ^^^^^
 - Bug in :meth:`Series.replace` and :meth:`DataFrame.replace` when replacing timezone-aware timestamps using a dict-like replacer (:issue:`27720`)
--
+- Bug in :meth:`Series.rename` when using a custom type indexer. Now any value that isn't callable or dict-like is treated as a scalar. (:issue:`27814`)
 -
 -
 

pandas/core/series.py

@@ -4164,12 +4164,10 @@ def rename(self, index=None, **kwargs):
         """
         kwargs["inplace"] = validate_bool_kwarg(kwargs.get("inplace", False), "inplace")
 
-        non_mapping = is_scalar(index) or (
-            is_list_like(index) and not is_dict_like(index)
-        )
-        if non_mapping:
+        if callable(index) or is_dict_like(index):
+            return super().rename(index=index, **kwargs)
+        else:
             return self._set_name(index, inplace=kwargs.get("inplace"))
-        return super().rename(index=index, **kwargs)
 
     @Substitution(**_shared_doc_kwargs)
     @Appender(generic.NDFrame.reindex.__doc__)

pandas/tests/series/test_alter_axes.py

@@ -267,6 +267,19 @@ def test_rename_axis_none(self, kwargs):
         expected = Series([1, 2, 3], index=expected_index)
         tm.assert_series_equal(result, expected)
 
+    def test_rename_custom_indexer(self):
+        # GH 27814
+        class MyIndexer:
+            pass
+
+        ix1, ix2 = MyIndexer(), MyIndexer()
+        s = Series([1, 2, 3])
+        s = s.rename(ix1)
+        assert s.name is ix1
+
+        s.rename(ix2, inplace=True)
+        assert s.name is ix2
+
     def test_set_axis_inplace_axes(self, axis_series):
         # GH14636
         ser = Series(np.arange(4), index=[1, 3, 5, 7], dtype="int64")