{"id":3124,"date":"2021-11-29T07:55:07","date_gmt":"2021-11-29T07:55:07","guid":{"rendered":"https:\/\/www.pythontutorial.net\/?page_id=3124"},"modified":"2021-12-09T10:12:46","modified_gmt":"2021-12-09T10:12:46","slug":"python-regular-expressions","status":"publish","type":"page","link":"https:\/\/www.pythontutorial.net\/python-regex\/python-regular-expressions\/","title":{"rendered":"Python Regular Expressions"},"content":{"rendered":"\n

Summary<\/strong>: in this tutorial, you’ll learn about Python regular expressions and how to use the most commonly used regular expression functions.<\/p>\n\n\n\n

Introduction to the Python regular expressions #<\/a><\/h2>\n\n\n\n

Regular expressions (called regex or regexp) specify search patterns. Typical examples of regular expressions are the patterns for matching email addresses, phone numbers, and credit card numbers.<\/p>\n\n\n\n

Regular expressions are essentially a specialized programming language embedded in Python. And you can interact with regular expressions via the built-in re<\/code> module in Python.<\/p>\n\n\n\n

\"\"<\/figure><\/div>\n\n\n\n

The following shows an example of a simple regular expression:<\/p>\n\n\n

'\\d'<\/span><\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Note that you’ll learn how to construct more complex and advanced patterns in the next tutorials. This tutorial focuses on the functions that deal with regular expressions.<\/p>\n\n\n\n
To use this regular expression, you follow these steps:<\/p>\n\n\n\n
First, import the re<\/code> module:<\/p>\n\n\n
import<\/span> re<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Second, compile the regular expression into a Pattern<\/code> object:<\/p>\n\n\n
p = re.compile('\\d'<\/span>)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Third, use one of the methods of the Pattern<\/code> object to match a string:<\/p>\n\n\n
s = \"Python 3.10 was released on October 04, 2021\"<\/span>\nresult = p.findall(s)\n\nprint(result)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Output:<\/p>\n\n\n
['3'<\/span>, '1'<\/span>, '0'<\/span>, '0'<\/span>, '4'<\/span>, '2'<\/span>, '0'<\/span>, '2'<\/span>, '1'<\/span>]<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
The findall()<\/code> method returns a list of single digits in the string s. <\/p>\n\n\n\n
The following shows the complete program:<\/p>\n\n\n
import<\/span> re\n\n\np = re.compile('\\d'<\/span>)\ns = \"Python 3.10 was released on October 04, 2021\"<\/span>\n\nresults = p.findall(s)\nprint(results)<\/code><\/span>Code language:<\/span> Python<\/span> (<\/span>python<\/span>)<\/span><\/small><\/pre>\n\n\n
Besides the findall()<\/code> method, the Pattern<\/code> object has other essential methods that allow you to match a string:<\/p>\n\n\n\n
Method<\/th>Purpose<\/th><\/tr><\/thead>
match()<\/a><\/code><\/td>Find the pattern at the beginning of a string<\/td><\/tr>
search()<\/code><\/td>Return the first match of a pattern in a string<\/td><\/tr>
findall()<\/code><\/td>Return all matches of a pattern in a string<\/td><\/tr>
finditer()<\/code><\/td>Return all matches of a pattern as an iterator<\/a><\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n
Python regular expression functions #<\/a><\/h2>\n\n\n\n
Besides the Pattern<\/code> class, the re<\/code> module has some functions that match a string for a pattern:<\/p>\n\n\n\n
In this example, a regular expression is a string that contains a search pattern. The '\\d'<\/code> is a digit character set<\/a> that matches any single digit from 0 to 9. <\/p>\n\n\n\n