Python Regex Sets & Ranges

Summary: in this tutorial, you’ll learn how to use the sets and ranges to create patterns that match a set of characters.

Several characters or character sets inside square brackets [] mean matching for any character or character set among them.

Sets

For example, [abc] means any of three characters. 'a', 'b', or 'c'. The [abc] is called a set. And you can use the set with regular characters to construct a search pattern.

For example, the following program uses the pattern licen[cs]e that matches both license and licence:

import re

s = 'A licence or license'

pattern = 'licen[cs]e'
matches = re.finditer(pattern, s)

for match in matches:
    print(match.group())Code language: PHP (php)

Output:

licence
license

The pattern licen[cs]e searches for:

• licen
• then one of the letters [cs]
• then e.

Therefore, it matches license and licence.

Ranges

When a set consists of many characters in e.g., from a to z or 1 to 9, it’ll tedious to list them in a set. Instead, you can use character ranges in square brackets. For example, [a-z] is a character in the range from a to z and [0-9] is a digit from 0 to 9.

Also, you can use multiple ranges within the same square brackets. For example, [a-z0-9] has two ranges that match for a character that is either from a to z or a digit from 0 to 9.

Similarly, you can use one or more character sets inside the square brackets like [\d\s] means a digit or a space character.

Likewise, you can mix the character with character sets. For example, [\d_] matches for a digit or an underscore.

Excluding sets & ranges

To negate a set or a range, you use the caret character (^) at the beginning of the set and range. For example, the range [^0-9] matches any character except a digit. It is the same as the character set \D.

Notice that regex also uses the caret (^) as an anchor that matches at the beginning of a string. However, if you use the caret (^) inside the square brackets, the regex will treat it as a negation operator, not an anchor.

The following example uses the caret (^) to negate the set [aeoiu] to match the consonants in the string 'Python':

import re

s = 'Python'

pattern = '[^aeoiu]'
matches = re.finditer(pattern, s)

for match in matches:
    print(match.group())
Code language: JavaScript (javascript)

Output:

P
y
t
h
n

Summary

• A set or a range matches any single character or character set specified in square brackets […].
• Use the caret (^) operator to negate a set or a range like [^...].