[Tut] Python | Split String with Regex

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[Tut] Python | Split String with Regex - xSicKxBot - 12-13-2022

Python | Split String with Regex

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Summary: The different methods to split a string using regex are:

re.split()
re.sub()
re.findall()
re.compile()

[b]Minimal Example[/b]

Code:
import re text = "Earth:Moon::Mars:Phobos" # Method 1
res = re.split("[:]+", text)
print(res) # Method 2
res = re.sub(r':', " ", text).split()
print(res) # Method 3
res = re.findall("[^:\s]+", text)
print(res) # Method 4
pattern = re.compile("[^:\s]+").findall
print(pattern(text)) # Output
['Earth', 'Moon', 'Mars', 'Phobos']

Problem Formulation

Problem: Given a string and a delimiter. How will you split the string using the given delimiter using different functions from the regular expressions library?

Example: In the following example, the given string has to be split using a hyphen as the delimiter.

Code:
# Input
text = "abc-lmn-xyz" # Expected Output
['abc', 'lmn', 'xyz']

Method 1: re.split

The

Code:
re.split(pattern, string)

method matches all occurrences of the

Code:
pattern

in the

Code:
string

and divides the string along the matches resulting in a list of strings between the matches. For example,

Code:
re.split('a', 'bbabbbab')

results in the list of strings

Code:
['bb', 'bbb', 'b']

Approach: Use the

Code:
re.split

function and pass

Code:
[_]+

as the pattern which splits the given string on occurrence of an underscore.

Code:

Code:
import re text = "abc_lmn_xyz"
res = re.split("[_]+", text)
print(res) # ['abc', 'lmn', 'xyz']

Related Read: Python Regex Split

Method 2: re.sub

The regex function

Code:
re.sub(P, R, S)

replaces all occurrences of the pattern

Code:
P

with the replacement

Code:
R

in string

Code:
S

. It returns a new string. For example, if you call

Code:
re.sub('a', 'b', 'aabb')

, the result will be the new string

Code:
'bbbb'

with all characters

Code:
'a'

replaced by

Code:
'b'

Approach: The idea here is to use the

Code:
re.sub

function to replace all occurrences of underscores with a space and then use the split function to split the string at spaces.

Code:

Code:
import re text = "abc_lmn_xyz"
res = re.sub(r'_', " ", text).split()
print(res) # ['abc', 'lmn', 'xyz']

Related Read: Python Regex Sub

Method 3: re.findall

The

Code:
re.findall(pattern, string)

method scans

Code:
string

from left to right, searching for all non-overlapping matches of the

Code:
pattern

. It returns a list of strings in the matching order when scanning the string from left to right.

[Image: image-168.png]

Approach: Find all occurrences of characters that are separated by underscores using the

Code:
re.findall()

.

Code:

Code:
import re text = "abc_lmn_xyz"
res = re.findall("[^_\s]+", text)
print(res) # ['abc', 'lmn', 'xyz']

Related Read: Python re.findall()

Method 4: re.compile

The method

Code:
re.compile(pattern)

returns a regular expression object from the

Code:
pattern

that provides basic regex methods such as

Code:
pattern.search(string)

Code:
pattern.match(string)

, and

Code:
pattern.findall(string)

. The explicit two-step approach of (1) compiling and (2) searching the pattern is more efficient than calling, say,

Code:
search(pattern, string)

at once, if you match the same pattern multiple times because it avoids redundant compilations of the same pattern.

[Image: image-170.png]

Code:

Code:
import re text = "abc_lmn_xyz"
pattern = re.compile("[^-\s]+").findall
print(pattern(text)) # ['abc', 'lmn', 'xyz']

[b]Why use re.compile?[/b]

Efficiency: Using
Code:
re.compile()
to assemble regular expressions is effective when the expression has to be used more than once. Thus, by using the classes/objects created by compile function, we can search for instances that we need within different strings without having to rewirte the expressions again and again. This increases productivity as well as saves time.
Readability: Another advantage of using
Code:
re.compile
is the readability factor as it leverages you the power to decouple the specification of the regex.

Read: Is It Worth Using Python’s re.compile()?

[b]Exercise[/b]

Problem: Python regex split by spaces, commas, and periods, but not in cases like 1,000 or 1.50.

Given:

Code:
my_string = "one two 3.4 5,6 seven.eight nine,ten"

Expected Output:

Code:
["one", "two", "3.4", "25.6" , "seven", "eight", "nine", "ten"]

Solution

Code:
my_string = "one two 3.4 25.6 seven.eight nine,ten"
res = re.split('\s|(?<!\d)[,.](?!\d)', my_string)
print(res) # ['one', 'two', '3.4', '25.6', 'seven', 'eight', 'nine', 'ten']

Conclusion

Therefore, we have learned four different ways of splitting a string using the regular expressions package in Python. Feel free to use the suitable technique that fits your needs. The idea of this tutorial was to get you acquainted with the numerous ways of using regex to split a string and I hope it helped you.

Please stay tuned and subscribe for more interesting discussions and tutorials in the future. Happy coding!

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