Twisted Async

Twisted is a mature, event-driven networking library for Python that abstracts away the complexity of socket programming and concurrent I/O. Instead of threading or multiprocessing, Twisted uses a reactor (single-threaded event loop) and Deferreds (callback chains) to handle thousands of concurrent connections efficiently. You write Protocol classes (handlers for each connection), Factory classes (producers of protocols), and register them with Twisted's reactor. The reactor listens for socket events, dispatches them to your handlers, and manages backpressure automatically. Twisted includes built-in support for HTTP, SSH, Telnet, SMTP, IMAP, DNS, and more, plus a powerful testing framework (trial) for integration tests.