Scheduling tasks for the future

Let's say we want to run a task X seconds in the future. The way to do that is defined in the reactor interface twisted.internet.interfaces.IReactorTime:

from twisted.internet import reactor

def f(s):
    print "this will run 3.5 seconds after it was scheduled: %s" % s

reactor.callLater(3.5, f, "hello, world")

# f() will only be called if the event loop was started:
reactor.run()

If we want a task to run every X seconds repeatedly, we can use twisted.internet.task.LoopingCall:

from twisted.internet import task

def runEverySecond():
    print "a second has passed"

l = task.LoopingCall(runEverySecond)
l.start(1.0) # call every second

# l.stop() will stop the looping calls
reactor.run()

If we want to cancel a task that we've scheduled:

from twisted.internet import reactor

def f():
    print "I'll never run."

callID = reactor.callLater(5, f)
callID.cancel()
reactor.run()

As with all reactor-based code, in order for scheduling to work the reactor must be started using reactor.run().