[Twisted-Python] LoopingCall and object instances

Hello, I have got following code: hosts = ['google.com','yahoo.com'] for host in hosts: c = PingContext(num, host) ctx.append(c) l = task.LoopingCall(c.ping) l.start(30.0, False) I create a few object instances and pinging those hosts every 30 secs. I will have another loop through LoopingCall, where I will be checking dynamically changing list and comparing with already been checking hosts. If there is a host missing in the list I will delete the object instance which is not in the list. How can I remove it that it will not be anymore called by LoopingCall? Or how can I add a new object instance to the LoopingCall in case there is new host in the list? Hopefully, it's understandable. Thank you, Lada