# Read username, output from non-empty factory, drop connections
# Use deferreds, to minimize synchronicity assumptions
# Write application. Save in 'finger.tpy'
from twisted.application import internet, service
from twisted.internet import protocol, reactor, defer
from twisted.protocols import basic
class FingerProtocol(basic.LineReceiver):
    def lineReceived(self, user):
        self.factory.getUser(user
        ).addErrback(lambda _: "Internal error in server"
        ).addCallback(lambda m:
                      (self.transport.write(m+"\r\n"),
                       self.transport.loseConnection()))
class FingerFactory(protocol.ServerFactory):
    protocol = FingerProtocol
    def __init__(self, **kwargs): self.users = kwargs
    def getUser(self, user):
        return defer.succeed(self.users.get(user, "No such user"))

application = service.Application('finger', uid=1, gid=1)
factory = FingerFactory(moshez='Happy and well')
internet.TCPServer(79, factory).setServiceParent(
    service.IServiceCollection(application))