Python Standard Library

The re Module

“Some people, when confronted with a problem, think ‘I know, I’ll use regular expressions.’ Now they have two problems.”

—Jamie Zawinski, on comp.lang.emacs

The re module provides a set of powerful regular expression facilities, which allows you to quickly check whether a given string matches a given pattern (using the match function), or contains such a pattern (using the search function). A regular expression is a string pattern written in a compact (and quite cryptic) syntax.

The match function attempts to match a pattern against the beginning of the given string, as shown in Example 1-54. If the pattern matches anything at all (including an empty string, if the pattern allows that!), match returns a match object. The group method can be used to find out what matched.

Example 1-54. Using the re Module to Match Strings

File: re-example-1.py

import re

text = "The Attila the Hun Show"

# a single character
m = re.match(".", text)
if m: print repr("."), "=>", repr(m.group(0))

# any string of characters
m = re.match(".*", text)
if m: print repr(".*"), "=>", repr(m.group(0))

# a string of letters (at least one)
m = re.match("\w+", text)
if m: print repr("\w+"), "=>", repr(m.group(0))

# a string of digits
m = re.match("\d+", text)
if m: print repr("\d+"), "=>", repr(m.group(0))

'.' => 'T'
'.*' => 'The Attila the Hun Show'
'\\w+' => 'The'

You can use parentheses to mark regions in the pattern. If the pattern matched, the group method can be used to extract the contents of ...