Refinements

Author: rhshadrach

doc/source/whatsnew/v3.0.0.rst

@@ -380,7 +380,7 @@ In cases with mixed-resolution inputs, the highest resolution is used:
 When all objects passed to :func:`concat` have a :class:`DatetimeIndex`,
 passing ``sort=False`` will now result in the non-concatenation axis not
 being sorted. Previously, the result would always be sorted along
-the non-concatenation axis even when ``sort=False`` is passed.
+the non-concatenation axis even when ``sort=False`` is passed. :issue:`57335`
 
 If you do not specify the ``sort`` argument, pandas will continue to return a
 sorted result but this behavior is deprecated and you will receive a warning.

pandas/core/indexes/api.py

@@ -182,7 +182,7 @@ def safe_sort_index(index: Index) -> Index:
     return index
 
 
-def union_indexes(indexes, sort: bool | None | lib.NoDefault = True) -> Index:
+def union_indexes(indexes, sort: bool | lib.NoDefault = True) -> Index:
     """
     Return the union of indexes.
 

pandas/core/reshape/concat.py

@@ -422,8 +422,7 @@ def concat(
             intersect
             or any(not isinstance(index, DatetimeIndex) for index in non_concat_axis)
             or all(
-                id(prev) == id(curr)
-                for prev, curr in zip(non_concat_axis, non_concat_axis[1:])
+                prev is curr for prev, curr in zip(non_concat_axis, non_concat_axis[1:])
             )
             or (
                 all(