Parentheses for Grouping and Capturing with Regex
One of the ways of pattern matching with Regex is by using Parentheses around the patterns. Let us see a few different examples for a better understanding.
Matching Objects
Say you want to separate the area code from the rest of the phone number. Adding parentheses will create groups in the regex: (\d\d\d)-(\d\d\d-\d\d\d\d). Then you can use the group() match object method to grab the matching text from just one group.
Python3
import re phoneNumRegex = re.compile(r'(\d\d\d)-(\d\d\d-\d\d\d\d)') mo = phoneNumRegex.search('My number is 415-555-4242.') print(mo.group(1)) areaCode, number = mo.groups() print("area code:", areaCode) print("number:", number) |
Output:
415
area code: 415
number: 555-4242
Retrieve all the Groups at Once
If you would like to retrieve all the groups at once, use the groups(), method—note the plural form for the name.
Python3
import re phoneNumRegex = re.compile(r'(\d\d\d)-(\d\d\d-\d\d\d\d)') mo = phoneNumRegex.search('My number is 415-555-4242.') print(mo.groups()) |
Output:
('415', '555-4242')
Match a parenthesis
Parentheses have a special meaning in regular expressions, but what do you do if you need to match a parenthesis in your text. For instance, maybe the phone numbers you are trying to match have the area code set in parentheses. In this case, you need to escape the ( and ) characters with a backslash. Enter the following into the interactive shell:
Python3
import re phoneNumRegex = re.compile(r'(\(\d\d\d\)) (\d\d\d-\d\d\d\d)') mo = phoneNumRegex.search('My phone number is (415) 555-4242.') print(mo.group(1)) |
Output:
(415)
The \( and \) escape characters in the raw string passed to re.compile() will match actual parenthesis characters.
Pattern matching in Python with Regex
You may be familiar with searching for text by pressing ctrl-F and typing in the words you’re looking for. Regular expressions go one step further: They allow you to specify a pattern of text to search for. In this article, we will see how pattern matching in Python works with Regex.