#6932: remove paragraph that advises relying on __del__ being called.

Doc/library/shelve.rst

@@ -30,27 +30,39 @@ lots of shared  sub-objects.  The keys are ordinary strings.
 
    Because of Python semantics, a shelf cannot know when a mutable
    persistent-dictionary entry is modified.  By default modified objects are
-   written only when assigned to the shelf (see :ref:`shelve-example`).  If
-   the optional *writeback* parameter is set to *True*, all entries accessed
-   are cached in memory, and written back at close time; this can make it
-   handier to mutate mutable entries in the persistent dictionary, but, if
-   many entries are accessed, it can consume vast amounts of memory for the
-   cache, and it can make the close operation very slow since all accessed
-   entries are written back (there is no way to determine which accessed
-   entries are mutable, nor which ones were actually mutated).
+   written only when assigned to the shelf (see :ref:`shelve-example`).  If the
+   optional *writeback* parameter is set to *True*, all entries accessed are
+   cached in memory, and written back on :meth:`sync` and :meth:`close`; this
+   can make it handier to mutate mutable entries in the persistent dictionary,
+   but, if many entries are accessed, it can consume vast amounts of memory for
+   the cache, and it can make the close operation very slow since all accessed
+   entries are written back (there is no way to determine which accessed entries
+   are mutable, nor which ones were actually mutated).
+
+   .. note::
+
+      Do not rely on the shelf being closed automatically; always call
+      :meth:`close` explicitly when you don't need it any more, or use a
+      :keyword:`with` statement with :func:`contextlib.closing`.
+
 
 Shelf objects support all methods supported by dictionaries.  This eases the
 transition from dictionary based scripts to those requiring persistent storage.
 
-One additional method is supported:
-
+Two additional methods are supported:
 
 .. method:: Shelf.sync()
 
-   Write back all entries in the cache if the shelf was opened with *writeback* set
-   to *True*. Also empty the cache and synchronize the persistent dictionary on
-   disk, if feasible.  This is called automatically when the shelf is closed with
-   :meth:`close`.
+   Write back all entries in the cache if the shelf was opened with *writeback*
+   set to :const:`True`.  Also empty the cache and synchronize the persistent
+   dictionary on disk, if feasible.  This is called automatically when the shelf
+   is closed with :meth:`close`.
+
+.. method:: Shelf.close()
+
+   Synchronize and close the persistent *dict* object.  Operations on a closed
+   shelf will fail with a :exc:`ValueError`.
+
 
 .. seealso::
 
@@ -75,11 +87,6 @@ Restrictions
   database should be fairly small, and in rare cases key collisions may cause the
   database to refuse updates.
 
-* Depending on the implementation, closing a persistent dictionary may or may
-  not be necessary to flush changes to disk.  The :meth:`__del__` method of the
-  :class:`Shelf` class calls the :meth:`close` method, so the programmer generally
-  need not do this explicitly.
-
 * The :mod:`shelve` module does not support *concurrent* read/write access to
   shelved objects.  (Multiple simultaneous read accesses are safe.)  When a
   program has a shelf open for writing, no other program should have it open for