Code examples of Twisted

Twisted makes it easy to implement custom network applications. Here's a TCP server that echoes back everything that's written to it:

from twisted.internet import protocol, reactor, endpoints

class Echo(protocol.Protocol):
    def dataReceived(self, data):
        self.transport.write(data)

class EchoFactory(protocol.Factory):
    def buildProtocol(self, addr):
        return Echo()

endpoints.serverFromString(reactor, "tcp:1234").listen(EchoFactory())
reactor.run()

Twisted includes an event-driven web server. Here's a sample web application; notice how the resource object persists in memory, rather than being recreated on each request:

from twisted.web import server, resource
from twisted.internet import reactor, endpoints

class Counter(resource.Resource):
    isLeaf = True
    numberRequests = 0

    def render_GET(self, request):
        self.numberRequests += 1
        request.setHeader("content-type", "text/plain")
        return "I am request #" + str(self.numberRequests) + "\n"

endpoints.serverFromString(reactor, "tcp:8080").listen(server.Site(Counter()))
reactor.run()

Here's a simple publish/subscribe server, where clients see all messages posted by other clients:

from twisted.internet import reactor, protocol, endpoints
from twisted.protocols import basic

class PubProtocol(basic.LineReceiver):
    def __init__(self, factory):
        self.factory = factory

    def connectionMade(self):
        self.factory.clients.add(self)

    def connectionLost(self, reason):
        self.factory.clients.remove(self)

    def lineReceived(self, line):
        for c in self.factory.clients:
            c.sendLine("<{}> {}".format(self.transport.getHost(), line))

class PubFactory(protocol.Factory):
    def __init__(self):
        self.clients = set()

    def buildProtocol(self, addr):
        return PubProtocol(self)

endpoints.serverFromString(reactor, "tcp:1025").listen(PubFactory())
reactor.run()

You can test this out by opening two terminals and doing telnet localhost 1025 in each, then typing things.