What Are Python Regular Expressions? See Examples

Regular expressions (regex) in Python allow you to search, match, and manipulate text based on patterns. They are powerful for string validation, data extraction, and text processing.

Python provides the re module to work with regex:

import re

Why Regular Expressions Are Important

Validate input (emails, phone numbers, passwords)
Search and extract data from text
Replace or format strings efficiently
Essential in real-world applications like web scraping, log parsing, and data cleaning

Example 1: Basic Matching

import re

pattern = r"\d+"  # Matches one or more digits
text = "There are 15 apples and 20 oranges."
matches = re.findall(pattern, text)
print(matches)  # Output: ['15', '20']

Example 2: Validating an Email Address

import re

email = "example@gmail.com"
pattern = r"^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+\.[a-zA-Z0-9-.]+$"

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

Useful for user input validation in real-world applications

Example 3: Replacing Text Using Regex

import re

text = "Contact us at support@example.com"
new_text = re.sub(r"\S+@\S+", "[email protected]", text)
print(new_text)  # Output: Contact us at [email protected]

Allows masking sensitive data in logs or reports

Example 4: Real-World Scenario – Extracting Phone Numbers

import re

text = "Call me at 123-456-7890 or 987-654-3210"
pattern = r"\d{3}-\d{3}-\d{4}"
phones = re.findall(pattern, text)
print(phones)  # Output: ['123-456-7890', '987-654-3210']

Useful for data extraction from documents, emails, or websites

Best Practices

✔ Compile regex patterns using re.compile() for performance
✔ Keep patterns readable and documented
✔ Test regex using online tools or Python console
✔ Avoid overly complex patterns to maintain clarity

Conclusion

Python regular expressions are a powerful tool for text processing. Mastering regex allows you to validate, extract, and manipulate textual data efficiently, which is crucial in real-world applications like data cleaning, web scraping, and automation.

References

Internal Reference: https://savanka.com/category/learn/python/
External Reference: https://www.w3schools.com/python/