Regular Expressions

Published Aug 1, 2021Updated Jul 2, 2023

Regex, short for regular expressions, is a powerful system for searching text. Regular expressions are implemented in a variety of languages including Java and Python.

Syntax

Regular expressions are accessed by importing the re module:

import re

regex = r"this is a regex pattern"

For the most part, regex patterns are expressed with raw string notation (hence, the preceding r character).

The following entries explore some terms and operations related to Python regular expressions:

Regular Expressions

Metacharacters: Matches or qualifies regular character patterns or other expressions.
re.findall(): Returns a list of every pattern match that occurs in a given string.
re.match(): Returns a matching character pattern at the beginning of a given string.
re.search(): Returns the first match of a character pattern anywhere in a given string.
re.split(): Divides a string into substrings at each occurrence of the specified character(s).
re.sub(): Replace matching substrings with a new string for all occurrences, or a specified number.