Programming Python, Second Edition

File Tools

External files are at the heart of much of what we do with shell utilities. For instance, a testing system may read its inputs from one file, store program results in another file, and check expected results by loading yet another file. Even user interface and Internet-oriented programs may load binary images and audio clips from files on the underlying computer. It’s a core programming concept.

In Python, the built-in open function is the primary tool scripts use to access the files on the underlying computer system. Since this function is an inherent part of the Python language, you may already be familiar with its basic workings. Technically, open gives direct access to the stdio filesystem calls in the system’s C library -- it returns a new file object that is connected to the external file, and has methods that map more or less directly to file calls on your machine. The open function also provides a portable interface to the underlying filesystem -- it works the same on every platform Python runs on.

Other file-related interfaces in Python allow us to do things such as manipulate lower-level descriptor-based files (module os), store objects away in files by key (modules anydbm and shelve), and access SQL databases. Most of these are larger topics addressed in Chapter 16. In this section, we take a brief tutorial look at the built-in file object, and explore a handful of more advanced file-related topics. As usual, you should consult the library manual’s file object ...