Python Regex-intro
Table of Contents
Description
Regular Expressions (Regex) are patterns used to match sequences of characters in strings. Python provides the built-in re module to perform regex operations such as searching, matching, splitting, and replacing. Regex helps in validating inputs (e.g., emails), extracting specific patterns (e.g., dates, phone numbers), and text cleaning.
Prerequisites
- Basic string manipulation
- Python functions and modules
- Understanding of pattern matching logic
Examples
Here's a simple program in Python:
✅ Basic Regex Match
import re
# Check if 'python' is in the string
text = "I love python programming"
match = re.search(r"python", text)
if match:
print("Match found!") # Output: Match found!
✅ Pattern Matching with Digits
# Check if the string has 3 digits
result = re.match(r"\d{3}", "123abc")
print(result.group()) # Output: 123
✅ Find All Matches
# Find all words in the sentence
text = "Python is easy to learn"
words = re.findall(r"\w+", text)
print(words) # Output: ['Python', 'is', 'easy', 'to', 'learn']
✅ Substitution
# Replace digits with #
text = "My number is 9876543210"
masked = re.sub(r"\d", "#", text)
print(masked) # Output: My number is ##########
✅ Splitting a String
# Split by any space or punctuation
text = "Hello, world! Welcome to Python."
parts = re.split(r"[\s,.!]+", text)
print(parts) # Output: ['Hello', 'world', 'Welcome', 'to', 'Python', '']
Real-World Applications
Form validation (emails, phone numbers, passwords)
Data cleaning in Data Science
Log file parsing
Web scraping (extracting structured data)
Syntax highlighting and lexical analysis
Where topic Can Be Applied
Web development (user input validation)
Natural Language Processing (NLP) and text preprocessing
Data pipelines (ETL systems)
Search engines (pattern-based search)
Security systems (filtering malicious patterns)
Resources
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Interview Questions
What is the purpose of re.search() vs re.match()?
What does \d, \w, \s, . mean in regex?
How would you extract all email addresses from a document?
How do you replace all special characters from a string?
Explain the difference between greedy and non-greedy matching.
How do you split a string based on multiple delimiters?
What is the use of ^ and $ in regular expressions?
How would you write a regex for validating a strong password?
Can regex be used to validate nested structures like HTML?
How does regex help in data preprocessing for ML?