“Use the Source, Luke”

The preceding chapter introduced Python’s client-side Internet tool set—the standard library modules available for email, FTP, network news, and more, from within a Python script. This chapter picks up where the last one left off and presents a complete client-side example—PyMailGUI, a Python program that sends, receives, composes, and parses Internet email messages.

Although the end result is a working program that you can actually use for your email, this chapter also has a few additional agendas worth noting before we get started:

Client-side scripting

For one thing, PyMailGUI implements a full-featured GUI that runs on your machine, and communicates with your mail servers when necessary. As such, it is a network client program that further illustrates some of the preceding chapter’s topics, and it will help us contrast server-side solutions introduced in the next chapter.

Code reuse

Additionally, PyMailGUI ties together a number of the utility modules we’ve been writing in the book so far, and demonstrates the power of code reuse in the process—it uses a thread module to allow mail transfers to overlap in time, a set of mail modules to process message content and route it across networks, a window protocol module to handle icons, and so on. Moreover, it inherits the power of tools in the Python standard library, such as the email package; message construction and parsing, for example, is trivial here.

Programming in the large

And finally, because PyMailGUI is a relatively large-scale program (at least as Python programs go), it shows by example some of the code structuring techniques that come in handy once we leave the realm of the small. Object-oriented programming (OOP) and modular design work well here to divide the system in smaller, self-contained units.

Ultimately, though, PyMailGUI serves to illustrate just how far the combination of GUIs, networking, and Python can take us. Like all Python programs, this system is scriptable—once you’ve learned its general structure, you can easily change it to work as you like, by modifying its source code. And like all Python programs, this one is portable across platforms—you can run it on any system with Python and a network connection, without having to change its code. Such advantages become automatic when your software is coded in an open source, portable, and readable language like Python.