Python Regular Expression Syntax Explained Simply

This article explains how to work with Regular Expressions (RegEx) in Python using the "re" module. RegEx is a sequence of characters that defines a search pattern.

Below are different ways to use RegEx in Python. These are some of the essential methods in Python's re module that help with pattern matching, searching, replacing, and extracting data efficiently.

• Using the re.match() method

• Using the re.findall() method

• Using the re.search() method

• Using the re.sub() and re.subn() methods

• Using the re.split() method

Using re.match() Method

The re.match() method checks if a string matches a given pattern at the beginning. In the example, we will check if the string 'abyss' starts with a pattern that has an 'a' followed by any three characters and ending with an 's'. in case of a match, it will show the message "Search successful."

import re

pattern = '^a...s$'
test_string = 'abyss'
result = re.match(pattern, test_string)

if result:
    print("Search successful.")
else:
    print("Search unsuccessful.")

Output

When you run the program, it will show this output -

Search successful.

Using re.findall() Method

The re.findall() method extracts all occurrences of a pattern in a string. In our example, we will look for all numbers (\d+) in the string 'hello 12 hi 89. Howdy 34' and get them into a list. It then prints all the numbers found.

import re

string = 'hello 12 hi 89. Hows you 34'
pattern = '\d+'
result = re.findall(pattern, string)
print("Numbers in the string:", result)

Output

After running the program, you will get this result -

Numbers in the string: ['12', '89', '34']

Using re.search() Method

The re.search() method looks for the first occurrence of a pattern in a string. This example will check if the string "Python is fun" starts with 'Python'. If yes, it displays "Pattern found inside the string."

import re

string = "Python is fun"
match = re.search('\APython', string)

if match:
    print("Pattern found inside the string.")
else:
    print("Pattern not found.")

Output

This output will be displayed when the program runs -

Pattern found inside the string.

Using re.sub() and re.subn() Methods

The re.sub() method replaces all occurrences of a pattern, while re.subn() does the same but also returns the number of substitutions. In this example, it will remove all spaces (\s+) from the string 'abc 12\ de 23 \n f45 6', which results in 'abc12de23f456'.

import re

string = 'abc 12\ de 23 \n f45 6'
pattern = '\s+'
replace = ''
new_string = re.sub(pattern, replace, string)
print(new_string)

Output

You will see this result after executing the program -

abc12de23f456

Using re.split() Method

The re.split() method splits a string at matches of the given pattern. Here, it splits the string 'Twelve:12 Eighty nine:89.' at each number (\d+). The output will be a list of parts of the string separated by the numbers.

import re

string = 'Twelve:12 Eighty nine:89.'
pattern = '\d+'
result = re.split(pattern, string)
print(result)

Output

The program gives this output when it is run -

['Twelve:', ' Eighty nine:', '.']