Python Regex Non-capturing Group

Summary: in this tutorial, you’ll learn about the Python regex non-capturing group to create a group but don’t want to store it in the groups of the match.

Introduction to the Python regex non-capturing group

Regular expressions have two types of groups:

  • Capturing groups
  • Non-capturing groups

So far, you learned how to use a capturing group to extract information from a bigger match or rematch the previous matched group using a backreference.

To do that, you create a capturing group, you place a pattern (or a rule) inside the parentheses, for example:

(X)
Code language: Python (python)

This syntax captures whatever match X inside the match so that you can access it via the group() method of the Match object.

Sometimes, you may want to create a group but don’t want to capture it in the groups of the match. To do that, you can use a non-capturing group with the following syntax:

(?:X)
Code language: Python (python)

Python Regex no-capturing group example

The following example illustrates how to use the capturing groups to capture the major and minor versions of Python in the string "Python 3.10"

import re s = 'Python 3.10' pattern = '(\d+)\.(\d+)' match = re.search(pattern, s) # show the whole match print(match.group()) # show the groups for group in match.groups(): print(group)
Code language: Python (python)

Output:

3.10 3 10
Code language: Python (python)

The following pattern matches one or more digits followed by the literal string (.) and one or more digits:

(\d+)\.(\d+)
Code language: Python (python)

It has two capturing groups. They capture the digits before and after the literal (.):

3 10
Code language: Python (python)

Suppose you don’t want to capture the digits before the literal character (.), you can use a non-capturing group like this:

import re s = 'Python 3.10' pattern = '(?:\d+)\.(\d+)' match = re.search(pattern, s) # show the whole match print(match.group()) # show the groups for group in match.groups(): print(group)
Code language: Python (python)

Output:

3.10 10
Code language: Python (python)

In this example, we use the non-capturing group for the first group:

(?:\d+)
Code language: Python (python)

To capture the minor version only, you can ignore the non-capturing group in the first place like this:

import re s = 'Python 3.10' pattern = '\d+\.(\d+)' match = re.search(pattern, s) # show the whole match print(match.group()) # show the groups for group in match.groups(): print(group)
Code language: Python (python)

Output:

3.10 10
Code language: Python (python)

So why do you use the non-capturing group anyway? the reason for using the non-capturing group is to save memory, as the regex engine doesn’t need to store the groups in the buffer.

Summary

  • Use the regex non-capturing group to create a group but don’t save it in the groups of the match.
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