bpo-24464: Deprecate sqlite3.enable_shared_cache

Doc/whatsnew/3.10.rst

@@ -462,6 +462,14 @@ Deprecated
   scheduled for removal in Python 3.12.
   (Contributed by Erlend E. Aasland in :issue:`42264`.)
 
+* ``sqlite3.enable_shared_cache`` is now deprecated, scheduled for removal in
+  Python 3.12.  The method is undocumented, and it's use is strongly
+  discouraged by the SQLite3 documentation.  See `the SQLite3 docs
+  <https://sqlite.org/c3ref/enable_shared_cache.html/>` for more details.  If
+  shared cache must be used, open the database in URI mode using the
+  ``cache=shared`` query parameter.
+  (Contributed by Erlend E. Aasland in :issue:`24464`.)
+
 
 Removed
 =======

Lib/sqlite3/dbapi2.py

@@ -84,6 +84,20 @@ def convert_timestamp(val):
 
 register_adapters_and_converters()
 
+# bpo-24464: enable_shared_cache was deprecated in Python 3.10.  It's
+# scheduled for removal in Python 3.12.
+_old_enable_shared_cache = enable_shared_cache
+def enable_shared_cache(enable):
+    import warnings
+    msg = ("""
+        enable_shared_cache is deprecated and will be removed in Python 3.12.
+        Shared cache is strongly discouraged by the SQLite 3 documentation.
+        If shared cache must be used, open the database in URI mode using
+        the cache=shared query parameter.
+    """)
+    warnings.warn(msg, DeprecationWarning, stacklevel=2)
+    return _old_enable_shared_cache
+
 # Clean up namespace
 
 del(register_adapters_and_converters)

Lib/sqlite3/test/dbapi.py

@@ -83,6 +83,13 @@ def CheckNotSupportedError(self):
                                    sqlite.DatabaseError),
                         "NotSupportedError is not a subclass of DatabaseError")
 
+    def CheckSharedCacheDeprecated(self):
+        for enable in (True, False):
+            with self.assertWarns(DeprecationWarning) as cm:
+                sqlite.enable_shared_cache(enable)
+            self.assertIn("dbapi.py", cm.filename)
+
+
 class ConnectionTests(unittest.TestCase):
 
     def setUp(self):

Misc/NEWS.d/next/Library/2020-12-30-14-56-25.bpo-24464.vbNVHe.rst

@@ -0,0 +1,3 @@
+``sqlite3.enable_shared_cache`` is now deprecated, scheduled for removal in
+Python 3.12.  The method is undocumented, and it's use is strongly
+discouraged by the SQLite3 documentation. Patch by Erlend E. Aasland