from twisted.internet import utils, reactor

def printTrueValue(val):
    print "/bin/true exits with rc=%d" % val
    output = utils.getProcessValue('/bin/false')
    output.addCallback(printFalseValue)

def printFalseValue(val):
    print "/bin/false exits with rc=%d" % val
    reactor.stop()

output = utils.getProcessValue('/bin/true')
output.addCallback(printTrueValue)
reactor.run()