Programming Python, 4th Edition

Chapter 19. Text and Language

“See Jack Hack. Hack, Jack, Hack”

In one form or another, processing text-based information is one of the more common tasks that applications need to perform. This can include anything from scanning a text file by columns to analyzing statements in a language defined by a formal grammar. Such processing usually is called parsing—analyzing the structure of a text string. In this chapter, we’ll explore ways to handle language and text-based information and summarize some Python development concepts in sidebars along the way. In the process, we’ll meet string methods, text pattern matching, XML and HTML parsers, and other tools.

Some of this material is advanced, but the examples are small to keep this chapter short. For instance, recursive descent parsing is illustrated with a simple example to show how it can be implemented in Python. We’ll also see that it’s often unnecessary to write custom parsers for each language processing task in Python. They can usually be replaced by exporting APIs for use in Python programs, and sometimes by a single built-in function call. Finally, this chapter closes by presenting PyCalc—a calculator GUI written in Python, and the last major Python coding example in this text. As we’ll see, writing calculators isn’t much more difficult than juggling stacks while scanning text.

Strategies for Processing Text in Python

In the grand scheme of things, there are a variety of ways to handle text processing and language analysis in ...