Programming Python, 4th Edition

Chapter 13. Client-Side Scripting

“Socket to Me!”

The preceding chapter introduced Internet fundamentals and explored sockets—the underlying communications mechanism over which bytes flow on the Net. In this chapter, we climb the encapsulation hierarchy one level and shift our focus to Python tools that support the client-side interfaces of common Internet protocols.

We talked about the Internet’s higher-level protocols in the abstract at the start of the preceding chapter, and you should probably review that material if you skipped over it the first time around. In short, protocols define the structure of the conversations that take place to accomplish most of the Internet tasks we’re all familiar with—reading email, transferring files by FTP, fetching web pages, and so on.

At the most basic level, all of these protocol dialogs happen over sockets using fixed and standard message structures and ports, so in some sense this chapter builds upon the last. But as we’ll see, Python’s protocol modules hide most of the underlying details—scripts generally need to deal only with simple objects and methods, and Python automates the socket and messaging logic required by the protocol.

In this chapter, we’ll concentrate on the FTP and email protocol modules in Python, and we’ll peek at a few others along the way (NNTP news, HTTP web pages, and so on). Because it is so prevalent, we will especially focus on email in much of this chapter, as well as in the two to follow—we’ll use tools and techniques ...