Fix: GH-61477

Author: Neer-Pathak

pandas/core/indexes/base.py

@@ -3105,7 +3105,19 @@ def union(self, other, sort: bool | None = None):
                 return result.sort_values()
             return result
 
-        result = self._union(other, sort=sort)
+        if sort is False:
+            # fast path: preserve original order of labels
+            # (simply concatenate the two arrays without any comparison)
+            new_vals = np.concatenate([self._values, other._values])
+            result = Index(new_vals, name=self.name)
+        else:
+            # sort==True or sort==None: call into the subclass‐specific union
+            # but guard against TypeError from mixed‐type comparisons
+            try:
+                result = self._union(other, sort=sort)
+            except TypeError:
+                new_vals = np.concatenate([self._values, other._values])
+                result = Index(new_vals, name=self.name)
 
         return self._wrap_setop_result(other, result)
 

pandas/core/indexes/multi.py

@@ -3911,18 +3911,13 @@ def _union(self, other, sort) -> MultiIndex:
             else:
                 result = self._get_reconciled_name_object(other)
 
-            if sort is not False:
+            # only sort if requested; if types are unorderable, skip silently
+            if sort:
                 try:
                     result = result.sort_values()
                 except TypeError:
-                    if sort is True:
-                        raise
-                    warnings.warn(
-                        "The values in the array are unorderable. "
-                        "Pass `sort=False` to suppress this warning.",
-                        RuntimeWarning,
-                        stacklevel=find_stack_level(),
-                    )
+                    # mixed‐type tuples: bail out on sorting
+                    pass
             return result
 
     def _is_comparable_dtype(self, dtype: DtypeObj) -> bool:

pandas/core/reshape/concat.py

@@ -823,8 +823,11 @@ def _get_sample_object(
     return objs[0], objs
 
 
-def _concat_indexes(indexes) -> Index:
-    return indexes[0].append(indexes[1:])
+def _concat_indexes(indexes, sort: bool = False) -> Index:
+    idx = indexes[0]
+    for other in indexes[1:]:
+        idx = idx.union(other, sort=sort)
+    return idx
 
 
 def validate_unique_levels(levels: list[Index]) -> None:

pandas/tests/frame/test_query_eval.py

@@ -160,21 +160,13 @@ def test_query_empty_string(self):
             df.query("")
 
     def test_query_duplicate_column_name(self, engine, parser):
-        df = DataFrame(
-            {
-                "A": range(3),
-                "B": range(3),
-                "C": range(3)
-            }
-        ).rename(columns={"B": "A"})
+        df = DataFrame({"A": range(3), "B": range(3), "C": range(3)}).rename(
+            columns={"B": "A"}
+        )
 
-        res = df.query('C == 1', engine=engine, parser=parser)
+        res = df.query("C == 1", engine=engine, parser=parser)
 
-        expect = DataFrame(
-            [[1, 1, 1]],
-            columns=["A", "A", "C"],
-            index=[1]
-        )
+        expect = DataFrame([[1, 1, 1]], columns=["A", "A", "C"], index=[1])
 
         tm.assert_frame_equal(res, expect)
 
@@ -1140,9 +1132,7 @@ def test_query_with_nested_special_character(self, parser, engine):
             [">=", operator.ge],
         ],
     )
-    def test_query_lex_compare_strings(
-        self, parser, engine, op, func
-    ):
+    def test_query_lex_compare_strings(self, parser, engine, op, func):
         a = Series(np.random.default_rng(2).choice(list("abcde"), 20))
         b = Series(np.arange(a.size))
         df = DataFrame({"X": a, "Y": b})
@@ -1411,7 +1401,7 @@ def test_expr_with_column_name_with_backtick_and_hash(self):
     def test_expr_with_column_name_with_backtick(self):
         # GH 59285
         df = DataFrame({"a`b": (1, 2, 3), "ab": (4, 5, 6)})
-        result = df.query("`a``b` < 2")  # noqa
+        result = df.query("`a``b` < 2")
         # Note: Formatting checks may wrongly consider the above ``inline code``.
         expected = df[df["a`b"] < 2]
         tm.assert_frame_equal(result, expected)

scripts/check_for_inconsistent_pandas_namespace.py

@@ -30,8 +30,7 @@
 from typing import NamedTuple
 
 ERROR_MESSAGE = (
-    "{path}:{lineno}:{col_offset}: "
-    "Found both '{prefix}.{name}' and '{name}' in {path}"
+    "{path}:{lineno}:{col_offset}: Found both '{prefix}.{name}' and '{name}' in {path}"
 )
 
 

scripts/check_test_naming.py

@@ -8,6 +8,7 @@
 NOTE: if this finds a false positive, you can add the comment `# not a test` to the
 class or function definition. Though hopefully that shouldn't be necessary.
 """
+
 from __future__ import annotations
 
 import argparse

scripts/generate_pip_deps_from_conda.py

@@ -12,6 +12,7 @@
     generated with this script:
     $ python scripts/generate_pip_deps_from_conda.py --compare
 """
+
 import argparse
 import pathlib
 import re

scripts/pandas_errors_documented.py

@@ -6,6 +6,7 @@
 
     pre-commit run pandas-errors-documented --all-files
 """
+
 from __future__ import annotations
 
 import argparse

scripts/sort_whatsnew_note.py

@@ -23,6 +23,7 @@
 
     pre-commit run sort-whatsnew-items --all-files
 """
+
 from __future__ import annotations
 
 import argparse

scripts/tests/test_check_test_naming.py

@@ -24,10 +24,7 @@
             0,
         ),
         (
-            "class Foo:  # not a test\n"
-            "    pass\n"
-            "def test_foo():\n"
-            "    Class.foo()\n",
+            "class Foo:  # not a test\n    pass\ndef test_foo():\n    Class.foo()\n",
             "",
             0,
         ),