Introduction to Computing Using Python: An Application Development Focus

CHAPTER 4

Text Data, Files, and Exceptions

4.1 Strings, Revisited

4.2 Formatted Output

4.3 Files

4.4 Errors and Exceptions

4.5 Case Study: Logging File Access

Chapter Summary

Solutions to Practice Problems

Exercises

Problems

IN THIS CHAPTER, we focus on the Python tools and problem-solving patterns for processing text and files.

We take a running start by continuing the discussion of the string class we began in Chapter 2. We discuss, in particular, the extensive set of string methods that give Python powerful text-processing capabilities. We then go over the text-processing tools Python provides to control the format of output text.

After having mastered text processing, we cover files and file input/output (I/O) (i.e., how to read from and write to files from within a Python program).

Much of today's computing involves the processing of text content stored in files. We define several patterns for reading files that prepare the file content for processing.

Working with data coming interactively from the user or from a file introduces a source of errors for our program that we cannot really control. We go over the common errors that can occur. Finally, in this chapter's case study, we showcase the text-processing and I/O concepts introduced in the chapter in the context of an application that logs accesses to files.

4.1 Strings, Revisited

In Chapter 2 we introduced the string class str. Our goal then was to show that Python supported values other than numbers. We showed how string ...