chapter-14.1-regular-expressions.md

Table of Contents

Chapter 14 Introduction to Regular Expressions

res: https://docs.python.org/3/library/re.html

Python has a standard library for regular expressions called re module. The re module provides us regular expression matching operations.

Both Unicode Strings and Byte Strings can be searched using regular expressions in python however both cannot be mixed.

Regular Expressions contain even wider range of escape characters to represent different patterns inside strings.

Let us suppose we have the sentence:

str_1 = 'Regular expressions are better pattern matchers.'

Example 1: If we want to match all er from the above string like shown below:

> Regular expressions are bett`er` patt`er`n match`er`s.

We can match the regular expression by specyfing regex string as: `r'er'`

Example 2: If we want to match all er and ar from the above string like shown below:

Regular expressions are better pattern matchers.

We can match the regular expression by specifying regex string as: r'[ae]r'

Example 3: If we want to match all the occurence that start with J and end with n from the following expression:

str_1 = 'John, Jane, Jennifer, Joan, Jon, Adam, Eve'

We can match the regular expression by specifying regex string as: r'J\w*n' which results in matching the following:

John, Jane, Jennifer, Joan, Jon, Adam, Eve'

The example code snippet would be:

import re
str_1 = 'John, Jane, Jennifer, Joan, Jon, Adam, Eve'
print(re.findall(r'J\w*n', str_1))

# ['John', 'Jan', 'Jenn', 'Joan', 'Jon']

In above examples, we can see ordinary characters like J, n, etc. and special characters like ., \, [ ], etc. A combination of those characters creates a regular expression.

For Example

• "Ap+le" matches words Aple, Apple, Appple, etc.
• "b..k" matches words book, beak, b ok, etc.