Explain the Python RegEx with Example

Explain the Python RegEx with Example

What is RegEx?

RegEx (Regular Expression) is a pattern-matching language used to find, search, or manipulate text (strings).

Python has a built-in module for RegEx:

import re

Common RegEx Functions in Python (`re` module)

Function	Description
`re.match()`	Matches pattern only at the beginning of a string
`re.search()`	Searches for a pattern anywhere in the string
`re.findall()`	Returns all matches in a list
`re.finditer()`	Returns iterator of match objects
`re.sub()`	Replaces matches with another string
`re.split()`	Splits a string by the pattern

Basic Syntax

Symbol	Meaning	Example	Matches
`.`	Any character (except newline)	`a.c`	“abc”, “axc”
`^`	Start of string	`^Hello`	“Hello world”
`$`	End of string	`world$`	“Hello world”
`*`	0 or more repetitions	`go*d`	“gd”, “god”, “good”
`+`	1 or more repetitions	`go+d`	“god”, “good”
`?`	0 or 1 repetition	`go?d`	“gd”, “god”
`{n}`	Exactly n times	`\d{3}`	“123”
`{n,m}`	Between n and m times	`\d{2,4}`	“12”, “1234”
`[]`	Any one of listed characters	`[aeiou]`	Any vowel
`\d`	Any digit	`\d`	“0–9”
`\w`	Any word char (a–z, A–Z, 0–9, _)	`\w+`	“hello123”
`\s`	Any whitespace	`\s`	“ ”, “\t”
`	`	OR	`cat
`()`	Group	`(ab)+`	“abab”

Examples

1. Search for a Word

import re

text = "Python is powerful"
match = re.search("powerful", text)

if match:
    print("Found:", match.group())

Output:

Found: powerful

2. Check if String Starts with “Hello”

import re

text = "Hello World"
if re.match("^Hello", text):
    print("Starts with Hello")

Output:

Starts with Hello

3. Find All Numbers

import re

text = "Order numbers: 123, 456, and 789"
numbers = re.findall(r"\d+", text)
print(numbers)

Output:

['123', '456', '789']

4. Replace Text

import re

text = "I love Java"
result = re.sub("Java", "Python", text)
print(result)

Output:

I love Python

5. Split by Non-Alphabetic Characters

import re

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

Output:

['apple', 'banana', 'orange', 'grape']

6. Validate Email Example

import re

email = "user.name@example.com"
pattern = r"^[\w\.-]+@[\w\.-]+\.\w+$"

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

Output:

Valid email

Match Object Details

If a match is found using re.search() or re.match(), it returns a match object.

Example:

import re

text = "My number is 9876543210"
match = re.search(r"\d+", text)

if match:
    print("Matched text:", match.group())
    print("Start index:", match.start())
    print("End index:", match.end())

Output:

Matched text: 9876543210
Start index: 13
End index: 23

Summary

Use Case	Function	Example
Find a word	`re.search()`	`re.search("word", text)`
Find all matches	`re.findall()`	`re.findall(r"\d+", text)`
Replace text	`re.sub()`	`re.sub("old", "new", text)`
Split text	`re.split()`	`re.split(r"\s+", text)`
Validate pattern	`re.match()`	`re.match(r"^[A-Za-z]+$", text)`

2 Answers

Mayank kumar Verma 14 Oct 2025

Regex is a super smart search tool to finding patterns in text like email, phone number etc.

Basic stepup

pythone

4 Main Functions You Need

1 Find if exists - re. search ()

Python

text = “My number is 9876543210”

2 Find ALL

python

re.findall(r'\d+', “I have 2 cats, 3 dogs”) # ['2', ‘3’,]

3 Replace

re.sub(r'\d', 'X', "Call 123") # Call XXX

Key Patterns:

\d = digit (0-9)

\w = letter

\s = space

+ = one or more

Example

emport re

text = "Email: john@site.com"

email = re.findall(r'\S+@\S+', text)

print(email) #[ ‘jhon@site.com’ ]

Done.

Anubhav Sharma 13 Oct 2025

Function	Description
`re.match()`	Matches pattern only at the beginning of a string
`re.search()`	Searches for a pattern anywhere in the string
`re.findall()`	Returns all matches in a list
`re.finditer()`	Returns iterator of match objects
`re.sub()`	Replaces matches with another string
`re.split()`	Splits a string by the pattern

Symbol	Meaning	Example	Matches
`.`	Any character (except newline)	`a.c`	“abc”, “axc”
`^`	Start of string	`^Hello`	“Hello world”
`$`	End of string	`world$`	“Hello world”
`*`	0 or more repetitions	`go*d`	“gd”, “god”, “good”
`+`	1 or more repetitions	`go+d`	“god”, “good”
`?`	0 or 1 repetition	`go?d`	“gd”, “god”
`{n}`	Exactly n times	`\d{3}`	“123”
`{n,m}`	Between n and m times	`\d{2,4}`	“12”, “1234”
`[]`	Any one of listed characters	`[aeiou]`	Any vowel
`\d`	Any digit	`\d`	“0–9”
`\w`	Any word char (a–z, A–Z, 0–9, _)	`\w+`	“hello123”
`\s`	Any whitespace	`\s`	“ ”, “\t”
`	`	OR	`cat
`()`	Group	`(ab)+`	“abab”

Use Case	Function	Example
Find a word	`re.search()`	`re.search("word", text)`
Find all matches	`re.findall()`	`re.findall(r"\d+", text)`
Replace text	`re.sub()`	`re.sub("old", "new", text)`
Split text	`re.split()`	`re.split(r"\s+", text)`
Validate pattern	`re.match()`	`re.match(r"^[A-Za-z]+$", text)`

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Explain the Python RegEx with Example

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2 Answers

What is RegEx?

Common RegEx Functions in Python (re module)

Basic Syntax

Examples

1. Search for a Word

2. Check if String Starts with “Hello”

3. Find All Numbers

4. Replace Text

5. Split by Non-Alphabetic Characters

6. Validate Email Example

Match Object Details

Summary

Common RegEx Functions in Python (`re` module)