#8855: add shelve security warning.

Doc/library/shelve.rst

@@ -43,6 +43,11 @@ lots of shared  sub-objects.  The keys are ordinary strings.
       :meth:`close` explicitly when you don't need it any more, or use a
       :keyword:`with` statement with :func:`contextlib.closing`.
 
+.. warning::
+
+   Because the :mod:`shelve` module is backed by :mod:`pickle`, it is insecure
+   to load a shelf from an untrusted source.  Like with pickle, loading a shelf
+   can execute arbitrary code.
 
 Shelf objects support all methods supported by dictionaries.  This eases the
 transition from dictionary based scripts to those requiring persistent storage.