Untwisting Python Network Programming, from O’ReillyNet.

This article introduces basic client-side networking using both core Python modules and the Twisted framework. For its example, I will show how to send, receive, and delete emails, and conduct Telnet sessions.

I have written two functionally equivalent examples, one using the core modules (mail-core.py) and another using Twisted (mail-twisted.py), with both start, stop, and interact with a server to process emails.

Here is outline:

core Python modules

• Sending Mails with smtplib
• Retrieving Emails with poplib
• Conducting Telnet with telnetlib

Twisted Way

• Sending Mails the Twisted Way
• Retrieving Mails with Twisted
• Doing Telnet with Twisted

When to Be Twisted?

The two functionally equivalent programs, one using Python core modules and the other using the Twisted framework, significantly differ from each other in terms of programming style and the amount of code. Then when should you use either of the two options?

For basic programs such as the command-line client of this example, the Python core networking modules are more desirable due to the simplicity and performance advantages. However, most real-world networking programs are very complex, and Twisted’s asynchronous programming model is more effective.

For example, BitTorrent, the popular peer-to-peer file sharing client that performs massive parallel downloading of data chunks from different sources, uses Twisted. Twisted also works well in programs with graphical user interface (GUI), because its asynchronous nature fits more seamlessly with the event-driven programming models of modern GUI frameworks. In fact, Twisted has integration with popular GUI frameworks including PyGTK, Qt, Tkinter, WxPython, and Win32.

The other area where Twisted shines is in server programming. A typical network server uses multithreading so that it can handle multiple clients concurrently. The asynchronous mechanism of Twisted alleviates the creation and handling of threads by server programs. In addition, Twisted provides several protocols on which to build new networking services, enabling rapid development of complex servers. One such project is Quotient, which adopts Twisted to build a multiprotocol messaging server that supports a variety of protocols and services including SMTP, POP3, IMAP, webmail, and SIP.

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