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 res = '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
10Code 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
10Code 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 res = '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
10Code 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 res = '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
10Code 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.