Hi, I'm trying to process several items in callback function writeLog d.addCallback(self.writeLog,g=g) see below. Can writeLog return DeferredList instead of Deferred? WriteLog should run several inserts into db (some of which may fail). Or am I completely wrong here? Thanks, Pet def getData(self, *args, **kwargs ): try: g = MyClass(self.db) d = self.getResult(params=kwargs['params'], g=g) if d: d.addCallback(self.sendResult) d.addErrback(log.err) d.addCallback(self.writeLog,g=g) d.addErrback(log.err) return d except Exception, e: log.msg('Unknown error in getData:', e) return False def writeLog(self, *args, **kwargs): g = kwargs['g'] dlist = [self.wLog(g, p) for p in g.list] d = DeferredList(dlist, consumeErrors=True).addCallback(log.err) return d def wLog(self, g, p): return self.db.runInteraction(g.insertLog,p)