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)

Compilation flags


When compiling a pattern string into a pattern object, it's possible to modify the standard behavior of the patterns. In order to do that, we have to use the compilation flags. These can be combined using the bitwise OR "|".

Flag

Python

Description

re.IGNORECASE or re.I

2.x

3.x

The pattern will match lower case and upper case.

re.MULTILINE or re.M

2.x

3.x

This flag changes the behavior of two metacharacters:

  • ^: Which now matches at the beginning of the string and at the beginning of each new line.

  • $: In this case, it matches at the end of the string and the end of each line. Concretely, it matches right before the newline character.

re.DOTALL or re.S

2.x

3.x

The metacharacter "." will match any character even the newline.

re.LOCALE or re.L

2.x

3.x

This flag makes \w, \W, \b, \B, \s, and \S dependent on the current locale.

"re.LOCALE just passes the character to the underlying C library. It really only works on bytestrings which have 1 byte per character. UTF...