Python in a Nutshell, 4th Edition

Chapter 10. Regular Expressions

Regular expressions (REs, aka regexps) let programmers specify pattern strings and perform searches and substitutions. Regular expressions are not easy to master, but they can be a powerful tool for processing text. Python offers rich regular expression functionality through the built-in re module. In this chapter, we thoroughly present all about Python’s REs.

Regular Expressions and the re Module

A regular expression is built from a string that represents a pattern. With RE functionality, you can examine any string and check which parts of the string, if any, match the pattern.

The re module supplies Python’s RE functionality. The compile function builds an RE object from a pattern string and optional flags. The methods of an RE object look for matches of the RE in a string or perform substitutions. The re module also exposes functions equivalent to an RE object’s methods, but with the RE’s pattern string as the first argument.

This chapter covers the use of REs in Python; it does not teach every minute detail about how to create RE patterns. For general coverage of REs, we recommend the book Mastering Regular Expressions, by Jeffrey Friedl (O’Reilly), offering thorough coverage of REs at both tutorial and advanced levels. Many tutorials and references on REs can also be found online, including an excellent, detailed tutorial in Python’s online docs. Sites like Pythex and regex101 let you test your REs interactively. Alternatively, you can start ...