From 16be119cc04d9327df78e0891bec40765bfd5d4f Mon Sep 17 00:00:00 2001
From: Federico Caselli <cfederico87@gmail.com>
Date: Thu, 9 Oct 2025 20:45:26 +0200
Subject: [PATCH] Improve typing and code in cursor module

Change-Id: I56b89f303f03dfc7056c7174ac06bc1679319bb5
---
 lib/sqlalchemy/engine/cursor.py | 47 +++++++++++++++------------------
 1 file changed, 22 insertions(+), 25 deletions(-)

diff --git a/lib/sqlalchemy/engine/cursor.py b/lib/sqlalchemy/engine/cursor.py
index 35d8180ac0..5fcc93150e 100644
--- a/lib/sqlalchemy/engine/cursor.py
+++ b/lib/sqlalchemy/engine/cursor.py
@@ -20,6 +20,7 @@ from typing import Any
 from typing import cast
 from typing import ClassVar
 from typing import Dict
+from typing import Final
 from typing import Iterable
 from typing import Iterator
 from typing import List
@@ -80,45 +81,45 @@ _Ts = TypeVarTuple("_Ts")
 # using raw tuple is faster than namedtuple.
 # these match up to the positions in
 # _CursorKeyMapRecType
-MD_INDEX: Literal[0] = 0
+MD_INDEX: Final[Literal[0]] = 0
 """integer index in cursor.description
 
 """
 
-MD_RESULT_MAP_INDEX: Literal[1] = 1
+MD_RESULT_MAP_INDEX: Final[Literal[1]] = 1
 """integer index in compiled._result_columns"""
 
-MD_OBJECTS: Literal[2] = 2
+MD_OBJECTS: Final[Literal[2]] = 2
 """other string keys and ColumnElement obj that can match.
 
 This comes from compiler.RM_OBJECTS / compiler.ResultColumnsEntry.objects
 
 """
 
-MD_LOOKUP_KEY: Literal[3] = 3
+MD_LOOKUP_KEY: Final[Literal[3]] = 3
 """string key we usually expect for key-based lookup
 
 this comes from compiler.RM_NAME / compiler.ResultColumnsEntry.name
 """
 
 
-MD_RENDERED_NAME: Literal[4] = 4
+MD_RENDERED_NAME: Final[Literal[4]] = 4
 """name that is usually in cursor.description
 
 this comes from compiler.RENDERED_NAME / compiler.ResultColumnsEntry.keyname
 """
 
 
-MD_PROCESSOR: Literal[5] = 5
+MD_PROCESSOR: Final[Literal[5]] = 5
 """callable to process a result value into a row"""
 
-MD_UNTRANSLATED: Literal[6] = 6
+MD_UNTRANSLATED: Final[Literal[6]] = 6
 """raw name from cursor.description"""
 
 
 _CursorKeyMapRecType = Tuple[
     Optional[int],  # MD_INDEX, None means the record is ambiguously named
-    int,  # MD_RESULT_MAP_INDEX
+    int,  # MD_RESULT_MAP_INDEX, -1 if MD_INDEX is None
     List[Any],  # MD_OBJECTS
     str,  # MD_LOOKUP_KEY
     str,  # MD_RENDERED_NAME
@@ -222,21 +223,17 @@ class CursorResultMetaData(ResultMetaData):
     def _splice_horizontally(self, other: CursorResultMetaData) -> Self:
         keymap = dict(self._keymap)
         offset = len(self._keys)
-        keymap.update(
-            {
-                key: (
-                    # int index should be None for ambiguous key
-                    (
-                        value[0] + offset
-                        if value[0] is not None and key not in keymap
-                        else None
-                    ),
-                    value[1] + offset,
-                    *value[2:],
-                )
-                for key, value in other._keymap.items()
-            }
-        )
+
+        for key, value in other._keymap.items():
+            # int index should be None for ambiguous key
+            if value[MD_INDEX] is not None and key not in keymap:
+                md_index = value[MD_INDEX] + offset
+                md_object = value[MD_RESULT_MAP_INDEX] + offset
+            else:
+                md_index = None
+                md_object = -1
+            keymap[key] = (md_index, md_object, *value[2:])
+
         self_tf = self._tuplefilter
         other_tf = other._tuplefilter
 
@@ -428,7 +425,7 @@ class CursorResultMetaData(ResultMetaData):
         # column keys and other names
         if num_ctx_cols:
             # keymap by primary string...
-            by_key = {
+            by_key: Dict[str, _CursorKeyMapRecType] = {
                 metadata_entry[MD_LOOKUP_KEY]: metadata_entry
                 for metadata_entry in raw
             }
@@ -474,7 +471,7 @@ class CursorResultMetaData(ResultMetaData):
                 # record into by_key.
                 by_key.update(
                     {
-                        key: (None, None, [], key, key, None, None)
+                        key: (None, -1, [], key, key, None, None)
                         for key in dupes
                     }
                 )
-- 
2.47.3