--- py3k/Lib/shelve.py.orig	2009-03-13 20:42:45.000000000 +0800
+++ py3k/Lib/shelve.py	2009-03-13 20:44:49.000000000 +0800
@@ -210,6 +210,32 @@
         Shelf.__init__(self, dbm.open(filename, flag), protocol, writeback)
 
 
+class FastDbfilenameShelf(DbfilenameShelf):
+    """Shelf implementation without cache sync when writeback=True.
+
+    This implementation will never write back cached entries. Thus there's no
+    delay during shelf close, but has potential data lose risk.
+
+    To avoid data lose, never do this even with writeback=True:
+
+      d['xx'] = range(4)  # this works as expected, but...
+      d['xx'].append(5)   # *this doesn't!* -- d['xx'] is STILL range(4)!!!
+
+    Instead always use:
+
+      temp = d['xx']      # extracts the copy
+      temp.append(5)      # mutates the copy
+      d['xx'] = temp      # stores the copy right back, to persist it
+    """
+
+    def __init__(self, filename, flag='c', protocol=None, writeback=True):
+        DbfilenameShelf.__init__(self, filename, flag, protocol, writeback)
+
+    def sync(self):
+        if hasattr(self.dict, 'sync'):
+            self.dict.sync()
+
+
 def open(filename, flag='c', protocol=None, writeback=False):
     """Open a persistent dictionary for reading and writing.