What it is
Twisted is an event-driven networking engine written in Python. It provides a robust framework for building asynchronous networked applications, including servers, clients, and protocols for TCP, UDP, SSL/TLS, and more.
Twisted uses an event-driven programming model where the reactor loop manages asynchronous events. Developers define protocols and factories to handle network events, such as connections, data received, and errors.
Installation
pip install twistedGetting started
The smallest useful thing you can do with it, and what each part means.
from twisted.internet import reactor, protocol
class Echo(protocol.Protocol):
def dataReceived(self, data):
self.transport.write(data)
class EchoFactory(protocol.Factory):
def buildProtocol(self, addr):
return Echo()
reactor.listenTCP(8000, EchoFactory())
reactor.run()from twisted.internet import reactor, protocol
class EchoClient(protocol.Protocol):
def connectionMade(self):
self.transport.write(b'Hello, world!')
def dataReceived(self, data):
print('Server said:', data)
self.transport.loseConnection()
class EchoFactory(protocol.ClientFactory):
def buildProtocol(self, addr):
return EchoClient()
def clientConnectionFailed(self, connector, reason):
print('Connection failed')
reactor.stop()
def clientConnectionLost(self, connector, reason):
reactor.stop()
reactor.connectTCP('localhost', 8000, EchoFactory())
reactor.run()Advanced usage
Where the library earns its place over a simpler alternative.
from twisted.internet import reactor, defer
def got_result(result):
print('Result:', result)
reactor.stop()
d = defer.Deferred()
d.addCallback(got_result)
d.callback('Hello Twisted')
reactor.run()from twisted.web.client import getPage
from twisted.internet import reactor
def print_result(result):
print(result)
reactor.stop()
getPage(b'http://httpbin.org/get').addCallback(print_result)
reactor.run()from twisted.internet import ssl, reactor
from twisted.internet.protocol import Protocol, ClientFactory
class SecureClient(Protocol):
def connectionMade(self):
self.transport.write(b'Secure Hello')
def dataReceived(self, data):
print('Received:', data)
self.transport.loseConnection()
class SecureFactory(ClientFactory):
def buildProtocol(self, addr):
return SecureClient()
reactor.connectSSL('localhost', 8000, SecureFactory(), ssl.ClientContextFactory())
reactor.run()Errors and fixes
The failures you are most likely to hit, and what actually resolves them.
- ConnectionRefusedError
- Ensure the server is running and reachable at the specified host and port.
- twisted.internet.error.ReactorNotRunning
- Check that reactor.run() has been called and not stopped prematurely.
- TimeoutError
- Use Twisted’s timeout mechanisms or Deferred timeouts to handle slow connections.
Best practices
- Use the reactor loop for all asynchronous operations.
- Leverage Deferreds for handling asynchronous callbacks and chaining operations.
- Use Factories to manage protocol instances and connections.
- Avoid blocking calls inside Twisted protocols; use threads or deferToThread for blocking operations.
- Use Twisted’s built-in protocols and utilities to simplify network programming.
Background
Why it exists, and what it was reacting to.
Twisted was created by Glyph Lefkowitz in 2002 to simplify the development of networked applications in Python. It focuses on asynchronous I/O, making it suitable for high-performance network servers and clients. Twisted supports multiple protocols out-of-the-box and has a flexible architecture for custom protocol implementation.