delavnog delavnog - 3 months ago 28
Python Question

How to combine callLater and addCallback?

This is so broken, I hope you are merciful with me:

reactor.callLater(0, myFunction, parameter1).addCallback(reactor.stop)
reactor.run()


myFunction
returns a deferred.

I hope it is clear what I want to do:


  • as soon as the reactor is running, I want to call
    myFunction
    . That is why I am using 0 as the delay parameter. Is there no other way except callLater? It looks funny to pass it a delay of 0.

  • I want to stop the reactor as soon as
    myFunction
    has completed the task.



The problems that I have so far:


  • AttributeError: DelayedCall instance has no attribute 'addCallback'
    . Fair enough! How do I put a callback in the callback chain started by
    myFunction
    then?

  • exceptions.TypeError: stop() takes exactly 1 argument (2 given)
    .



To solve the second problem I had to define a special function:

def stopReactor(result):
gd.log.info( 'Result: %s' % result)
gd.log.info( 'Stopping reactor immediatelly' )
reactor.stop()


And change the code to:

reactor.callLater(0, myFunction, parameter1).addCallback(stopReactor)
reactor.run()


(still not working because of the callLater problem, but
stopReactor
will work now)

Is there really no other way to call
reactor.stop
except by defining an extra function?

Answer

IReactorTime.callLater and Deferred are mixed together by twisted.internet.task.deferLater.

from twisted.internet import reactor, task

d = task.deferLater(reactor, 0, myFunction, parameter1)
d.addCallback(lambda _: reactor.stop())
reactor.run()