{"id":3139,"date":"2021-11-29T09:52:34","date_gmt":"2021-11-29T09:52:34","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=3139"},"modified":"2021-12-03T07:48:47","modified_gmt":"2021-12-03T07:48:47","slug":"python-regex-character-set","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-regex\/python-regex-character-set\/","title":{"rendered":"Python Regex Character Set"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you learn about character sets in regular expressions including digits, words, whitespace, and the dot (.).<\/p>\n\n\n\n

Introduction to Python regex character sets #<\/a><\/h2>\n\n\n\n

A character set (or a character class) is a set of characters, for example, digits (from 0 to 9), alphabets (from a to z), and whitespace.<\/p>\n\n\n\n

A character set allows you to construct regular expressions<\/a> with patterns that match a string with one or more characters in a set.<\/p>\n\n\n\n

\\d: digit character set #<\/a><\/h3>\n\n\n\n

Regular expressions use \\d<\/code> to represent a digit character set that matches a single digit from 0<\/code> to 9<\/code>.<\/p>\n\n\n\n

The following example uses the finditer()<\/code> function to match every single digit in a string using the \\d<\/code> character set:<\/p>\n\n\n

import<\/span> re\n\ns = 'Python 3.0 was released in 2008'<\/span>\nmatches = re.finditer('\\d'<\/span>, s)\nfor<\/span> match in<\/span> matches:\n    print(match.group())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
3<\/span>\n0<\/span>\n2<\/span>\n0<\/span>\n0<\/span>\n8<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
To match a group of two digits, you use the \\d\\d<\/code>. For example:<\/p>\n\n\n
import<\/span> re\n\ns = 'Python 3.0 was released in 2008'<\/span>\nmatches = re.finditer('\\d\\d'<\/span>, s)\nfor<\/span> match in<\/span> matches:\n    print(match.group())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
20<\/span>\n08<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Similarly, you can match a group of four digits using the \\d\\d\\d\\d<\/code> pattern:<\/p>\n\n\n
import<\/span> re\n\ns = 'Python 3.0 was released in 2008'<\/span>\nmatches = re.finditer('\\d\\d\\d\\d'<\/span>, s)\nfor<\/span> match in<\/span> matches:\n    print(match.group())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
2008<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
\\w: the word character set #<\/a><\/h3>\n\n\n\n
Regular expressions use \\w<\/code> to represent the word character set. The \\w<\/code> matches a single ASCII character including Latin alphabet, digit, and underscore (_<\/code>).<\/p>\n\n\n\n
The following example uses the finditer()<\/code> function to match every single word character in a string using the \\w<\/code> character set:<\/p>\n\n\n
import<\/span> re\n\ns = 'Python 3.0'<\/span>\nmatches = re.finditer('\\w'<\/span>, s)\nfor<\/span> match in<\/span> matches:\n    print(match.group())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
P\ny\nt\nh\no\nn\n3<\/span>\n0<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Notice that the whitespace and .<\/code> are not included in the matches.<\/p>\n\n\n\n
\\s : whitespace character set #<\/a><\/h3>\n\n\n\n
The \\s<\/code> matches whitespace including a space, a tab, a newline, a carriage return, and a vertical tab. <\/p>\n\n\n\n
The following example uses the whitespace character set to match a space in a string:<\/p>\n\n\n
import<\/span> re\n\ns = 'Python 3.0'<\/span>\nmatches = re.finditer('\\s'<\/span>, s)\nfor<\/span> match in<\/span> matches:\n    print(match)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
<re.Match object; span=(6<\/span>, 7<\/span>), match=' '<\/span>><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Inverse character sets #<\/a><\/h2>\n\n\n\n
A character set has an inverse character set that uses the same letter but in uppercase. The following table shows the character sets and their inverse ones:<\/p>\n\n\n\n
Character set<\/th>Inverse character set<\/th>Description<\/th><\/tr><\/thead>
\\d<\/code><\/td>\\D<\/code><\/td>Match a single character except for a digit<\/td><\/tr>
\\w<\/code><\/td>\\W<\/code><\/td>Match a single character that is not a word character<\/td><\/tr>
\\s<\/code><\/td>\\S<\/code><\/td>Match a single character except for whitespace<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
The following example uses the \\D<\/code> to match the non-digit from a phone number:<\/p>\n\n\n
import<\/span> re\n\nphone_no = '+1-(650)-513-0514'<\/span>\nmatches = re.finditer('\\D'<\/span>, phone_no)\nfor<\/span> match in<\/span> matches:\n    print(match.group())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
+\n-\n(\n)\n-\n-<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
To turn the phone number  +1-(650)-513-0514  into the 16505130514, you can use the sub() function:<\/p>\n\n\n
import<\/span> re\n\nphone_no = re.sub('\\D'<\/span>, ''<\/span>, '+1-(650)-513-0514'<\/span>)\nprint(phone_no)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
16505130514<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
In this example, the sub()<\/code> function replaces the character that matches the pattern \\D<\/code> with the literal string ''<\/code> in the formatted phone number. <\/p>\n\n\n\n
The dot(.) character set #<\/a><\/h3>\n\n\n\n
The dot (.<\/code>) character set matches any single character except the new line (\\n<\/code>). The following example uses the dot (.) character set to match every single character but the new line:<\/p>\n\n\n
import<\/span> re\n\nversion = \"Python\\n4\"<\/span>\nmatches = re.finditer('.'<\/span>, version)\nfor<\/span> match in<\/span> matches:\n    print(match.group())<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
P\ny\nt\nh\no\nn\n4<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Summary #<\/a><\/h2>\n\n\n\n
  • Use \\d<\/code> character set to match any single digit.<\/li>
  • Use \\w<\/code> character set to match any single word character.<\/li>
  • Use \\s<\/code> character set to match any whitespace.<\/li>
  • The \\D<\/code>, \\W<\/code>, \\S<\/code> character set are the inverse sets of \\d<\/code>, \\w<\/code>, and \\s<\/code> character set.<\/li>
  • Use the dot character set (.<\/code>) to match any character but a new line.<\/li><\/ul>\n
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Later, you’ll learn how to use quantifiers<\/a> to shorten the pattern. So instead of using the \\d\\d\\d\\d<\/code> pattern, you can use the shorter one like \\d{4}<\/code><\/p>\n\n\n\n