Queue class for Zeo

Supper cool in that i uses a decorator for the transaction commit
First time I actually used a decorator. I knew about them, but I never thought of a use for them. Ok I am slow :)

from persistent import Persistent
from BTrees.LOBTree import LOBTree
from ZODB.POSException import ConflictError
import Queue
import transaction
import time

def transactionDecorator(fn):
   def newfn(*args,**kwargs) :
       while 1 :
           try :
               transaction.manager.begin()
               result = fn(*args,**kwargs)
               transaction.manager.commit()
               return result
           except ConflictError:
               time.sleep(0.01)
           except Exception,e:
               transaction.manager.abort()
               raise e
   return newfn

class BTreeQueue(Persistent) :
   def __init__(self):
       self.bTree = LOBTree()
   @transactionDecorator
   def push(self,item):
       key = None
       try :
           key = self.bTree.maxKey()
       except ValueError :
           key = 0
       self.bTree.insert(key+1,item)
  
   @transactionDecorator
   def extend(self,items) :
       start = None
       try :
           start = self.bTree.maxKey()
       except ValueError :
           start = 0
       start += 1
       result = {}
       for i,key in enumerate(range(start,start+len(items))) :
           result[key] = items[i]
       self.bTree.update(result)
      
   @transactionDecorator
   def pop(self):
       item = None
       error = False
       try :
           key =self.bTree.minKey()
           item = self.bTree.pop(key)
       except ValueError :
           error = True
       finally :
           if error :
               raise Queue.Empty()
           else :
               return item

   @transactionDecorator
   def rotate(self):
       """pops a item then puts it on end again, returns value"""
       item = None
       error = False
       key =self.bTree.minKey()
       item = self.bTree.pop(key)
       self.bTree.insert(self.bTree.maxKey()+1,item)
       return item

   @transactionDecorator
   def count(self):
       count = None
       try :
           count = self.bTree.maxKey() - self.bTree.minKey() + 1
       except ValueError :
           count = 0
       return count
  
   @transactionDecorator
   def empty(self):
       self.bTree.clear()