gistfile1.txt

exarkun@baryon:~$ cat > /tmp/sscce.py
from twisted.internet import reactor
from twisted.internet.defer import Deferred, inlineCallbacks
from twisted.internet.task import deferLater
from twisted.internet.endpoints import serverFromString
from twisted.internet.protocol import Factory
from twisted.protocols.basic import LineReceiver


class _DomainLineReceiver(LineReceiver):

    delimiter = "\n"

    def lineReceived(self, line):
        deferLater(reactor, 1, self._output)

    def _output(self):
        print "PRINTED"
        self.sendLine("HEY COOL SILENT FAILURE")


endpoint = serverFromString(reactor, "stdio:")
endpoint.listen(Factory.forProtocol(_DomainLineReceiver))
reactor.run()

exarkun@baryon:~$ python /tmp/sscce.py 
hello
PRINTED
HEY COOL SILENT FAILURE