In Python (programming language), regular expressions (or regex) are used to search, match, and manipulate text based on patterns. They are extremely powerful for text processing, validation, and parsing.

Python provides the re module for working with regular expressions.

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1️⃣ Importing re Module

import re

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2️⃣ Basic Functions

re.search()

Searches for a pattern anywhere in the string. Returns a match object if found.

import re
text = "My phone number is 9876543210"
match = re.search(r"\d{10}", text)

if match:
    print("Phone number found:", match.group())

Output

Phone number found: 9876543210

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re.match()

Checks for a pattern at the beginning of the string.

text = "Python is fun"
match = re.match(r"Python", text)

if match:
    print("Match found:", match.group())

Output

Match found: Python

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re.findall()

Finds all occurrences of a pattern and returns a list.

text = "My numbers are 123 and 456"
numbers = re.findall(r"\d+", text)
print(numbers)

Output

['123', '456']

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re.sub()

Replaces matched patterns with new text.

text = "I like Java"
new_text = re.sub(r"Java", "Python", text)
print(new_text)

Output

I like Python

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3️⃣ Common Regex Patterns

Pattern	Description	Example
\d	Digit (0-9)	\d{3} matches 3 digits
\D	Non-digit	\D+ matches letters or symbols
\w	Alphanumeric	\w+ matches words
\W	Non-alphanumeric	\W+ matches symbols
\s	Whitespace	\s+ matches spaces, tabs
\S	Non-whitespace	\S+ matches non-space characters
.	Any character except newline	a.b matches a-b or aab
^	Start of string	^Hello
$	End of string	world$
*	0 or more	a*
+	1 or more	a+
?	0 or 1	a?
{n}	Exact n repetitions	\d{4} matches 4 digits
{n,m}	n to m repetitions	\d{2,4}

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4️⃣ Example: Email Validation

import re

email = "example@gmail.com"
pattern = r"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,}$"

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

Output

Valid email

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5️⃣ Example: Extract All Words

text = "Python, Java, C++"

words = re.findall(r"\w+", text)
print(words)

Output

['Python', 'Java', 'C']

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✅ Summary

Function	Purpose
re.search()	Search pattern anywhere
re.match()	Match pattern at start
re.findall()	Find all matches
re.sub()	Replace matched patterns

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⭐ Key Points

• Use raw strings r"pattern" to avoid escaping backslashes
• Regex is powerful for validation, searching, splitting, and replacing
• Learn common symbols like \d, \w, +, *, ^, $