[Twisted-Python] Run a function repeatedly at different intervals

Hi,

I am new to Twisted Python. I would like to fire a function several times at different intervals. For example, at 1 second fire f(), at 2 second fire f() again, at 4 second fire f(), and so on...

How do I do that? I looked at the doc and it has task.LoopingCall(second) but the time interval is fixed...

Thanks, Khoa