re-module.md

id	re-module
slug	/re-module
title	Re Module
description	Python regular expressions with the re module — pattern matching, searching, substitution, and how regex handling differs from JavaScript.
sidebar_label	Re Module

Regular expressions are powerful tools in programming languages for searching, matching, and manipulating text. The re module in Python provides support for regular expressions.

Task

Write a program that accepts a list of email addresses and uses regular expressions to extract the username and domain of each address.

JavaScript implementation

const emailAddresses = [
  "john.doe@example1.com",
  "jane.smith@example2.com",
  "foo@bar.com",
];

const regex = /([^@]+)@(.+)/;

emailAddresses.forEach((email) => {
  const [_, username, domain] = email.match(regex);
  console.log(`Username: ${username}, Domain: ${domain}`);
});

Python implementation:

import re

email_addresses = [
  "john.doe@example1.com",
  "jane.smith@example2.com",
  "foo@bar.com",
]

regex = re.compile(r"([^@]+)@(.+)")

for email in email_addresses:
  match = regex.match(email)
  if match:
    username, domain = match.groups()
    print(f"Username: {username}, Domain: {domain}")

:::tip In Python, prefixing a string with r indicates a raw string literal, which treats backslashes as literal characters. :::

Code Highlight

• In JavaScript, regular expressions can be defined using /.../ or new Regex(...), while in Python, you can create a regular expression using the re.compile() function.

Difference Quick View

Feature	JavaScript	Python
Creating a regular expression	const myReg = /pattern/; or new Regex(pattern)	my_regex = re.compile(r'pattern')
Matching a regular expression	myReg.test(myStr)	my_regex.match(my_str)
Finding the first match	myReg.exec(myStr)	my_regex.search(my_str)
Finding all matches	myStr.match(myReg)	my_regex.findall(my_str)
Replacing matches	myStr.replaceAll(myReg, replacement)	my_regex.sub(replacement, my_str)
Splitting a string using a regular expression	myStr.split(myReg)	my_regex.split(my_str)

:::tip In addition to using re.compile() to create a regular expression, you can also directly use methods like re.search() and re.split() from the re module to achieve the same functionality, such as:

import re

re.search(r'pattern', my_str)
re.split(r'pattern', my_str)

:::

Resources

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