Python Regex split()

Summary: in this tutorial, you’ll learn how to use the Python regex split() function to split a string at the occurrences of matches of a regular expression.

Introduction to the Python regex split() function

The built-in re module provides you with the split() function that splits a string by the matches of a regular expression.

The split() function has the following syntax:

split(pattern, string, maxsplit=0, flags=0)

In this syntax:

• pattern is a regular expression whose matches will be used as separators for splitting.
• string is an input string to split.
• maxsplit determines at most the splits occur. Generally, if the maxsplit is one, the resulting list will have two elements. If the maxsplit is two, the resulting list will have three elements, and so on.
• flags parameter is optional and defaults to zero. The flags parameter accepts one or more regex flags. The flags parameter changes how the regex engine matches the pattern.

The split() function returns a list of substrings split by the matches of the pattern in the string.

If the pattern contains one or more capturing groups, the split() function will return the text of all groups as elements of the resulting list.

If the pattern contains a capturing group that matches the start of a string, the split() function will return a resulting list with the first element being as an empty string. This logic is the same for the end of the string.

Python regex split() function examples

Let’s take some examples of using the regex split() function.

1) Using the split() function to split words in a sentence

The following example uses the split() function to split the words in a sentence:

import re

s = 'A! B. C D'
pattern = r'\W+'

l = re.split(pattern, s)
print(l)
Code language: JavaScript (javascript)

In this example, the \W+ is the inverse of the word character set that matches one or more characters that are not the word characters.

Output:

['A', 'B', 'C', 'D']Code language: JSON / JSON with Comments (json)

2) Using the split() function with the maxsplit argument

The following example uses the split() function that splits a string with two splits at non-word characters:

import re

s = 'A! B. C D'
pattern = r'\W+'

l = re.split(pattern, s, 2)
print(l)
Code language: JavaScript (javascript)

Output:

['A', 'B', 'C D']Code language: JSON / JSON with Comments (json)

Because we split the string with two splits, the resulting list contains three elements. Notice that the split() function returns the remainder of a string as the final element in the resulting list.

3) Using the split() function with a capturing group

The following example uses the split() function that splits a string with the \W+ pattern that contains a capturing group:

import re

s = 'A! B. C D'
pattern = r'(\W+)'

l = re.split(pattern, s, 2)
print(l)
Code language: JavaScript (javascript)

Output:

['A', '! ', 'B', '. ', 'C D']Code language: JSON / JSON with Comments (json)

In this example, the split() function also returns the text of the group in the resulting list.

4) Using the split() function

The following example uses the split() function where the separator contains a capturing group that matches the start of the string:

import re

s = '...A! B. C D'
pattern = r'\W+'

l = re.split(pattern, s)
print(l)Code language: JavaScript (javascript)

In this case, the split() function returns a list with the first element is an empty string:

['', 'A', 'B', 'C', 'D']Code language: JSON / JSON with Comments (json)

Similarly, if the separator contains the capturing groups and it matches the end of the string, the resulting list will have the last element as an empty string:

import re

s = 'A! B. C D...'
pattern = r'\W+'

l = re.split(pattern, s)
print(l)
Code language: JavaScript (javascript)

Output:

['A', 'B', 'C', 'D', '']Code language: JSON / JSON with Comments (json)

Summary

• Use the Python regex split() function to split a string using sepators as the matches of a regular expression.