Day 12: Python Programming

Regular Expressions (RegEx)

What is Regular Expression?
Regular Expression (RegEx) is a technique used to search, match, and manipulate text based on patterns.
In Python, RegEx is provided by re module.
import re

Why RegEx is Important?

• Validating emails, phone numbers
• Extracting IPs, URLs from logs
• Checking passwords
• Searching patterns
• Replacing characters
• Parsing large text files

Important Functions in re Module

Function	Description
re.search()	Returns first match
re.match()	Match only beginning of string
re.findall()	Returns all matches
re.split()	Split string using pattern
re.sub()	Replace text

Basic Patterns (Metacharacters)

Symbol	Meaning
.	Any character
^	Start of string
$	End of string
*	Zero or more times
+	One or more times
?	Zero or one
{n}	n times
{n,m}	n to m times
[]	Character set
\	Escape character
`	`	OR

Character Classes

Pattern	Meaning
\d	Digits (0–9)
\D	Non-digit
\w	Word (letters, numbers, _)
\W	Non-word
\s	Space
\S	Non-space

re.search() Example
import re
text = "Python is awesome"
result = re.search("awesome", text)
print(result)

Returns match object if found
re.findall() Example
import re
text = "cat rat mat fat"
print(re.findall("at", text))

Output:
['at', 'at', 'at', 'at']

re.match() Example
import re
print(re.match("Hello", "Hello World"))
Matches only at start.

re.split() Example
import re
text = "one,two,three"
print(re.split(",", text))

re.sub() Example (Replace)

import re
text = "Python is easy"
print(re.sub("easy", "powerful", text))

Pattern Matching Examples
1.Find all digits
re.findall(r"\d", "A1B2C3")

2.Find words starting with capital letter
re.findall(r"[A-Z][a-z]*", "India USA china Japan")

Email Validation Pattern

import re
email = "[e-mail]"
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")

Phone Number Validation (10 digits)

import re
num = "9876543210"
if re.fullmatch(r"\d{10}", num):
print("Valid Phone Number")

Password Validation

• At least 8 characters
• One uppercase
• One number

import re
pwd = "Abcd1234"
pattern = r"^(?=.[A-Z])(?=.\d).{8,}$"
if re.match(pattern, pwd):
print("Strong Password")

Extract IP Address
import re
log = "Error from 192.168.1.1 at 10:22 PM"
ip = re.findall(r"\d+.\d+.\d+.\d+", log)
print(ip)

Extract All Words
re.findall(r"\w+", "Python is super fast!")

Special Example: Find Vowels
re.findall(r"[aeiouAEIOU]", "Beautiful")

DevOps Use Case: Extract Error Lines from Log

import re
log = """
INFO: Started
ERROR: Disk Not Found
WARNING: Low Memory
ERROR: Service Down
errors = re.findall(r"ERROR.*", log)
print(errors)