Chapter 6. Complete System Programs

“The Greps of Wrath”

This chapter wraps up our look at the system interfaces domain in Python by presenting a collection of larger Python scripts that do real systems work—comparing and copying directory trees, splitting files, searching files and directories, testing other programs, configuring launched programs’ shell environments, and so on. The examples here are Python system utility programs that illustrate typical tasks and techniques in this domain and focus on applying built-in tools, such as file and directory tree processing.

Although the main point of this case-study chapter is to give you a feel for realistic scripts in action, the size of these examples also gives us an opportunity to see Python’s support for development paradigms like object-oriented programming (OOP) and reuse at work. It’s really only in the context of nontrivial programs such as the ones we’ll meet here that such tools begin to bear tangible fruit. This chapter also emphasizes the “why” of system tools, not just the “how”; along the way, I’ll point out real-world needs met by the examples we’ll study, to help you put the details in context.

One note up front: this chapter moves quickly, and a few of its examples are largely listed just for independent study. Because all the scripts here are heavily documented and use Python system tools described in the preceding chapters, I won’t go through all the code in exhaustive detail. You should read the source code listings ...

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