Explicitly mention that people should not depend on immediate

finalization of objects in the language reference.

Doc/reference/datamodel.rst

@@ -69,6 +69,8 @@ are still reachable.
    containing circular references.  See the documentation of the :mod:`gc`
    module for information on controlling the collection of cyclic garbage.
    Other implementations act differently and CPython may change.
+   Do not write code that depends on immediate finalization of objects
+   when they become unreachable (ex: always close your files).
 
 Note that the use of the implementation's tracing or debugging facilities may
 keep objects alive that would normally be collectable. Also note that catching