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 themaxsplit
is one, the resulting list will have two elements. If themaxsplit
is two, the resulting list will have three elements, and so on.flags
parameter is optional and defaults to zero. Theflags
parameter accepts one or more regex flags. Theflags
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 res = '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 res = '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 res = '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 res = '...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 res = '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.