bpo-45126: Deprecate sqlite3 Connection and Cursor reinitialization

Doc/whatsnew/3.11.rst

@@ -232,6 +232,10 @@ sqlite3
   (Contributed by Aviv Palivoda, Daniel Shahaf, and Erlend E. Aasland in
   :issue:`16379`.)
 
+* :class:`sqlite3.Connection` and :class:`sqlite3.Cursor` reinitialization is
+  now deprecated. Reinitialization will be disallowed in Python 3.13.
+  (Contributed by Erlend E. Aasland in :issue:`45126`.)
+
 
 Removed
 =======

Lib/sqlite3/test/dbapi.py

@@ -331,6 +331,13 @@ def test_drop_unused_refs(self):
             cu = self.cx.execute(f"select {n}")
             self.assertEqual(cu.fetchone()[0], n)
 
+    def test_connection_reinit(self):
+        db = ":memory:"
+        cx = sqlite.connect(db)
+        with self.assertWarns(DeprecationWarning) as cm:
+            cx.__init__(db)
+        self.assertIn("dbapi.py", cm.filename)
+
 
 class UninitialisedConnectionTests(unittest.TestCase):
     def setUp(self):
@@ -728,6 +735,13 @@ def test_same_query_in_multiple_cursors(self):
         for cu in cursors:
             self.assertEqual(cu.fetchall(), [(1,)])
 
+    def test_cursor_reinit(self):
+        db = ":memory:"
+        cu = self.cx.cursor()
+        with self.assertWarns(DeprecationWarning) as cm:
+            cu.__init__(self.cx)
+        self.assertIn("dbapi.py", cm.filename)
+
 
 class ThreadTests(unittest.TestCase):
     def setUp(self):

Misc/NEWS.d/next/Library/2021-09-08-12-36-38.bpo-45126.6N8Wzi.rst

@@ -0,0 +1,2 @@
+:class:`sqlite3.Connection` and :class:`sqlite3.Cursor` reinitialization is
+now deprecated. Reinitialization will be disallowed in Python 3.13.

Modules/_sqlite/connection.c

@@ -108,6 +108,15 @@ pysqlite_connection_init_impl(pysqlite_Connection *self,
         return -1;
     }
 
+    if (self->initialized) {
+        const char *msg = "Connection reinitialization is depreacted and will "
+                          "be disallowed in Python 3.13";
+        const int stacklevel = 1;
+        if (PyErr_WarnEx(PyExc_DeprecationWarning, msg, stacklevel) < 0) {
+            return -1;
+        }
+    }
+
     pysqlite_state *state = pysqlite_get_state_by_type(Py_TYPE(self));
     self->state = state;
 

Modules/_sqlite/cursor.c

@@ -50,6 +50,15 @@ pysqlite_cursor_init_impl(pysqlite_Cursor *self,
                           pysqlite_Connection *connection)
 /*[clinic end generated code: output=ac59dce49a809ca8 input=23d4265b534989fb]*/
 {
+    if (self->initialized) {
+        const char *msg = "Cursor reinitialization is depreacted and will be "
+                          "disallowed in Python 3.13";
+        const int stacklevel = 1;
+        if (PyErr_WarnEx(PyExc_DeprecationWarning, msg, stacklevel) < 0) {
+            return -1;
+        }
+    }
+
     Py_INCREF(connection);
     Py_XSETREF(self->connection, connection);
     Py_CLEAR(self->statement);