Python · Chapter 34 of 45

Regular Expressions

REGEX matches patterns in text. Python's `re` module provides `search`, `match`, `findall`, `sub` and more.

Common patterns: `\d` digit, `\w` word char, `\s` whitespace, `.` any char, `*` zero-or-more, `+` one-or-more.

Groups

Parentheses capture parts of the match. Access with `.group(n)` on a match object.

`re.sub(pattern, replacement, text)` replaces every match.

Example 1 (python)

import re
emails = re.findall(r"[\w.]+@[\w.]+", "contact us at hi@x.com or sales@y.io")
print(emails)

Output

['hi@x.com', 'sales@y.io']

Extract every email-like substring.

Example 2 (python)

import re
clean = re.sub(r"\s+", " ", "  too    many\n\tspaces  ").strip()
print(clean)

Output

too many spaces

Collapse whitespace.

💡 Note: Regex is powerful but hard to read. For simple splitting/replacing, plain string methods are clearer.