Hi, I need this for a project, so this is quite urgent. I got no answer to this until now, so I try again. Maybe somebody could tell me where to ask, if nobody knows a solution, tkanks. ------ I have two seperate processes communicating by Perspective Broker. One, the server, shall start an external program and send the output to the client. See code below. I get the following traceback (part of it): --------------------------------------------- File "/export/home/s/stfl/Twisted/twisted/spread/pb.py", line 472, in expressionReceived raise ProtocolError("Non-list expression received.") twisted.spread.pb.ProtocolError: Non-list expression received. Failure: twisted.spread.pb.PBConnectionLost: I've simplified the code to the following: server (listener.py): ----------------------- #!/usr/bin/env python from twisted.spread import pb from twisted.internet import reactor, app, protocol from twisted.cred import authorizer import os class ABPP(protocol.ProcessProtocol): def __init__(self, receiver): self.receiver = receiver def connectionMade(self): print "connection to client-prg made!" # XXX Here the error is triggered mydef = self.receiver.callRemote("receiveMessage", "connection made!") mydef.addCallback(self.t) def t(self, x): print 't:', x class ABListener(pb.Root): def __init__(self): self.receiver = None def remote_takeMessageReceiver(self, receiver): print 'self.receiver = receiver', receiver self.receiver = receiver def remote_dir(self): pp = ABPP(self.receiver) command = ['/bin/ls'] reactor.spawnProcess(pp, command[0], command, env=os.environ) reactor.run() if __name__ == '__main__': import listener ab_app = app.Application("ABListener") ab_app.listenTCP(8848, pb.BrokerFactory(ABListener())) ab_app.run(save=0) client (client.py) ----------------------- #!/usr/bin/env python from twisted.spread import pb from twisted.internet import reactor class MessageReceiver(pb.Referenceable): def remote_receiveMessage(self, message): print 'server echoed:', message, '<br>' class CComHandler: def __init__(self, mr): self.mr = mr self.remRef = None def gotObject(self, object): self.remRef = object mydef = self.remRef.callRemote("takeMessageReceiver", self.mr) mydef.addCallbacks(self.gaveMr, self.gotErr) def gaveMr(self, reason): print 'gave MessageReceiver' mydef = self.remRef.callRemote("dir") mydef.addCallbacks(self.calledDir, self.gotErr) def calledDir(self, reason): print 'called dir remotely<br>' def gotErr(self, reason): print 'Error: %s<br>' % reason reactor.stop() def doDir(): mr = MessageReceiver() c = CComHandler(mr) pb.getObjectAt("localhost", 8848, 30).addCallback(c.gotObject) reactor.run() if __name__ == "__main__": machine = 'mymachine' packages = [('myPackage', 'myVersion')] doDir()