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)

Non-capturing groups


As we've mentioned before, capturing content is not the only use of groups. There are cases when we want to use groups, but we're not interested in extracting the information; alternation would be a good example. That's why we have a way to create groups without capturing. Throughout this book, we've been using groups to create subexpressions, as can be seen in the following example:

>>>re.search("Españ(a|ol)", "Español")
<_sre.SRE_Match at 0x10e90b828>
>>>re.search("Españ(a|ol)", "Español").groups()
('ol',)

You can see that we've captured a group even though we're not interested in the content of the group. So, let's try it without capturing, but first we have to know the syntax, which is almost the same as in normal groups, (?:pattern). As you can see, we've only added ?:. Let's see the following example:

>>>re.search("Españ(?:a|ol)", "Español")
<_sre.SRE_Match at 0x10e912648>
>>>re.search("Españ(?:a|ol)", "Español").groups...