Book Image

Mastering Python Regular Expressions

Book Image

Mastering Python Regular Expressions

Overview of this book

Regular expressions are used by many text editors, utilities, and programming languages to search and manipulate text based on patterns. They are considered the Swiss army knife of text processing. Powerful search, replacement, extraction and validation of strings, repetitive and complex tasks are reduced to a simple pattern using regular expressions. Mastering Python Regular Expressions will teach you about Regular Expressions, starting from the basics, irrespective of the language being used, and then it will show you how to use them in Python. You will learn the finer details of what Python supports and how to do it, and the differences between Python 2.x and Python 3.x. The book starts with a general review of the theory behind the regular expressions to follow with an overview of the Python regex module implementation, and then moves on to advanced topics like grouping, looking around, and performance. You will explore how to leverage Regular Expressions in Python, some advanced aspects of Regular Expressions and also how to measure and improve their performance. You will get a better understanding of the working of alternators and quantifiers. Also, you will comprehend the importance of grouping before finally moving on to performance optimization techniques like the RegexBuddy Tool and Backtracking. Mastering Python Regular Expressions provides all the information essential for a better understanding of Regular Expressions in Python.
Table of Contents (12 chapters)

Building blocks for Python regex

In Python, there are two different objects dealing with Regex:

  • RegexObject: It is also known as Pattern Object. It represents a compiled regular expression

  • MatchObject: It represents the matched pattern


In order to start matching patterns, we'll have to compile the regex. Python gives us an interface to do that as we've seen previously. The result will be a pattern object or RegexObject. This object has several methods for typical operations on regular expressions. As we will see later, the re module provides a shorthand for every operation so that we can avoid compiling it first.

>>> pattern = re.compile(r'fo+')

The compilation of a regular expression produces a reusable pattern object that provides all the operations that can be done, such as matching a pattern and finding all substrings that match a particular regex. So, for example, if we want to know if a string starts with <HTML>, we can use the following code:

>>> pattern...