gh-135386: Fix dbm.sqlite3 readonly open error by using immutable=1

Author: blurb-it[bot]

Lib/dbm/sqlite3.py

@@ -69,6 +69,7 @@ def __init__(self, path, /, *, flag, mode):
             self._cx = sqlite3.connect(uri, autocommit=True, uri=True)
         except sqlite3.Error as exc:
             raise error(str(exc))
+        
         self._readonly = (flag == "ro")
         # This is an optimization only; it's ok if it fails.
         if not self._readonly:

Lib/test/test_dbm_sqlite3.py

@@ -1,3 +1,4 @@
+import os
 import sys
 import unittest
 from contextlib import closing
@@ -89,6 +90,22 @@ def test_readonly_keys(self):
     def test_readonly_iter(self):
         self.assertEqual([k for k in self.db], [b"key1", b"key2"])
 
+    def test_readonly_open_without_wal_shm(self):
+        wal_path = self.filename + "-wal"
+        shm_path = self.filename + "-shm"
+
+        for suffix in wal_path, shm_path:
+            try:
+                os.remove(suffix)
+            except FileNotFoundError:
+                pass
+
+        os.chmod(self.filename, 0o444)
+
+        with dbm_sqlite3.open(self.filename, "r") as db:
+            self.assertEqual(db[b"key1"], b"value1")
+            self.assertEqual(db[b"key2"], b"value2")
+
 
 class ReadWrite(_SQLiteDbmTests):
 

Misc/NEWS.d/next/Library/2025-06-16-15-00-13.gh-issue-135386.lNrxLc.rst

@@ -0,0 +1 @@
+Fix :exc:`sqlite3.OperationalError` error when using :func:`dbm.open` with a read-only file object.