RegEx

RegEx

A regular expression (regex) is a pattern for searching text. Python provides the re module.

Import and search

import re

txt = "The rain in Spain"
x = re.search("^The.*Spain
quot;, txt)

The search function

re.search() scans the whole string for a match and returns a match object (or None):

x = re.search("ai", txt)
print(x)  # <re.Match object...>

Common functions

• findall(): returns a list of all matches.
• search(): returns the first match as an object.
• split(): splits the string at matches.
• sub(): replaces matches.

print(re.findall("ai", txt))        # ['ai', 'ai']
print(re.split("\s", txt))          # split on whitespace
print(re.sub("Spain", "France", txt))# The rain in France

Metacharacters

Example with a set

print(re.findall("[a-m]", txt))  # letters a through m

Special sequences

• \d: digits.
• \s: whitespace.
• \w: word characters.
• \b: word boundary.

TL;DR

• Regex patterns search text with the re module.
• findall, search, split, sub are the main functions.
• Metacharacters shape the pattern.
• Use raw strings (r"...") to avoid escape confusion.