Explain split(), sub(), subn() methods of “re” module in Python

Regular expression

A Regular Expression or (RegEX) is a stream of characters that forms a pattern. Whether a string contains this pattern or not can be detected with the help of regular expressions. It’s very easy to create and use Regular Expressions in Python - by importing re module.

import re

split()

This function splits the string. It should be imported before using it in the program.

Example-1:

from re import split
print(split("\W+", "Words, words , Words"))

# Output:
['Words', 'words', 'Words']

Example-2: - Error

from re import split
# If you don't use this "\W+" 
# you will have a error 
# because is part of the function
print(split("Words, words , Words"))

# Output:
TypeError: split() missing 1 required positional argument: 'string'

Sub()

This function find all the substring where a certain regular expression matches and then replace them with a different string.

Syntax: - re.sub(pattern, repl, string, count=0, flags=0). count and flags are optionals.

import re

pattern = "[0-9]+"
repl = "NN"
string = "Account Number - 12345, Amount - 586.32"

print("Original string:")
print(string)

result = re.sub(pattern, repl, string)

print("After replacing:")
print(result)

# Output:

Original string:
Account Number - 12345, Amount - 586.32
After replacing:
Account Number - NN, Amount - NN.NN

subn()

This function is similar to sub() but the output is different. It returns a tuple with count of total of all the replacements.

import re

def add(m):
    # Convert.
    v = int(m.group(0))
    # Add 2.
    return str(v + 1)

# Call re.subn.
result = re.subn("\d+", add, "1 2 3 4 5")

print("Result string:", result[0])
print("Number of substitutions:", result[1])

Output

Result string: 11 21 31 41 51
Number of substitutions: 5

References

Official python documentation

Sub-Example

Subn

Regular expression