Regex in Python

Regular Expressions (Regex) are one of the most powerful tools in any programmer’s toolkit. In Python, they allow you to search, match, extract, replace, and validate patterns in text.

Whether you're cleaning data, validating user input, or parsing logs—Regex is your go-to tool for text processing.

A Regular Expression is a sequence of special characters that defines a search pattern.

For example:

• "a.b" → matches any character between a and b (like acb, arb, etc.)

• "\d+" → matches one or more digits (like 123, 42, etc.)

Using Regex in Python

Python provides the re module to work with regular expressions.

import re

Common Functions in the re Module

Function Description re.search() Searches for the first match re.match() Checks for a match only at the beginning re.findall() Returns all matches as a list re.sub() Replaces parts of the string re.split() Splits the string at matches

Search for an Email Address

import re

text = "Contact us at info@example.com"
pattern = r"\w+@\w+\.\w+"

match = re.search(pattern, text)
if match:
    print("Found:", match.group())

📤 Output:

Found: info@example.com

Regex Syntax: Important Symbols

Symbol Meaning Example Matches . Any character a.b a*b, a1b \d Digit \d+ 123, 42 \w Word character \w+ abc, user_1 \s Whitespace \s+ space, tab ^ Start of string ^Hi Matches if string starts with Hi $ End of string end$ Matches if string ends with end * 0 or more a* "", a, aaa + 1 or more a+ a, aa ? 0 or 1 a? "", a [] Character set [aeiou] any vowel OR `cat () Grouping (ab)+ abab

Validate a Phone Number

import re

number = "9876543210"
pattern = r"^\d{10}$"

if re.match(pattern, number):
    print("Valid phone number")
else:
    print("Invalid phone number")

📤 Output:

Valid phone number

Replacing with re.sub()

import re

text = "My email is user123@example.com"
clean_text = re.sub(r"\w+@\w+\.\w+", "[email hidden]", text)
print(clean_text)

📤 Output:

My email is [email hidden]

Splitting with re.split()

import re

data = "apple,banana;orange|grapes"
fruits = re.split(r"[,;|]", data)
print(fruits)

📤 Output:

['apple', 'banana', 'orange', 'grapes']