Python | Split String Parenthesis – Be on the Right Side of Change

🍎Summary: You can split a string at parenthesis using re.split(r'[()]', text) in a list comprehension accordingly.

Minimal Example

Problem Formulation

📜Problem: Given a string. How will you split the string at parenthesis and spaces?

Example

# Input
text = "abc xyz (ABC) (LMN) aabbcc"

# OUTPUT
['abc', 'xyz', 'ABC', 'LMN', 'aabbcc']

In the above problem, you have been given a string separated by spaces and there are certain strings that are within parenthesis. How will you achieve the expected output?

Method 1: Using re.split

Prerequisite: The re.split(pattern, string) method matches all occurrences of the pattern in the string and divides the string along the matches resulting in a list of strings between the matches. For example, re.split('a', 'bbabbbab') results in the list of strings ['bb', 'bbb', 'b'].

🪐Related Read: Python Regex Split

Approach: Use re.split(r'[()]', text) to split the string on the occurrence of a parenthesis. Here, the pattern [()] means whenever the script finds any parenthesis character it splits the string. Now, you will have a string containing substrings split at parenthesis. Your next task is to split the string at every occurrence of a whitespace. You can do that with the help of a simple split() function upon the previously computed value. However, this yields a list of lists that you can flatten using another list comprehension.

code

import re

text = "abc xyz (ABC) (LMN) aabbcc"
extract_parenthesis = [x for x in re.split(r'[()]', text) if x.strip()]
nested_result = [y.split() for y in extract_parenthesis]
res = [item for i in nested_result for item in i]
print(res)

# ['abc', 'xyz', '(ABC)', '(LMN)', 'aabbcc']

Explanation:

🪐Recommended Read: Flatten A List Of Lists In Python

Method 2: Using re.sub

Prerequisite: The regex function re.sub(P, R, S) replaces all occurrences of the pattern P with the replacement R in string S. It returns a new string. For example, if you call re.sub('a', 'b', 'aabb'), the result will be the new string 'bbbb' with all characters 'a' replaced by 'b'.

🪐Related Read: Python Regex Sub

Approach: The idea here is to substitute every occurrence of a parenthesis with an empty string. The entire string can then be split using the split() function.

Code

import re

text = "abc xyz (ABC) (LMN) aabbcc"
text_r = re.sub(r'[()]', "", text).split()
print(text_r)

# ['abc', 'xyz', '(ABC)', '(LMN)', 'aabbcc']

Method 3: Using re.findall

Prerequisite: The re.findall(pattern, string) method scans string from left to right, searching for all non-overlapping matches of the pattern. It returns a list of strings in the matching order when scanning the string from left to right.

🪐Related Read: Python re.findall() – Everything You Need to Know

Approach: Find all the items separated by parenthesis as well as whitespaces using the re.findall function. Use the “or”, i.e. “|” meta character to take care of both the conditions (strings within parenthesis and strings separated by whitespaces) at the same time.

Code

import re

text = "abc xyz (ABC) (LMN) aabbcc"
regex = r'\(.+?\)|".+?"|\w+'
result = re.findall(regex, text)
print(result)

# ['abc', 'xyz', '(ABC)', '(LMN)', 'aabbcc']

Conclusion

Hurrah! We have successfully split the given string at parenthesis and spaces. I hope this discussion was helpful and it answered all your queries. Please stay tuned and subscribe for more interesting reads and discussions.

Happy coding!

🪐Recommended Read: Python Regex to Return String Between Parentheses

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