Domain Name with Subdomain Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching domain name with subdomain, ported and verified for Python. A rigorously tested regex reduces debugging time and protects your application from edge-case failures. The snippet below is ready to drop into your Python project — whether you're validating in a Django view, a FastAPI endpoint, or a standalone data processing script.

Python Implementation

# Domain Name with Subdomain
# ReDoS-safe | RegexVault — Web & Network > Domain

import re

domain_name_with_subdomain_pattern = re.compile(r'^(?:[a-zA-Z0-9](?:[a-zA-Z0-9\-]{0,61}[a-zA-Z0-9])?\.){2,}[a-zA-Z]{2,63}$')

def validate_domain_name_with_subdomain(value: str) -> bool:
    return bool(domain_name_with_subdomain_pattern.fullmatch(value))

# Example
print(validate_domain_name_with_subdomain("www.example.com"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Domain category and carries a ReDoS-safe certification. That matters for Python developers because particularly important in Python web servers where CPU-bound regex operations can stall concurrent request handling. RegexVault audits patterns against known backtracking attack vectors, ensuring you have the necessary context before using this regex in a high-stakes production environment.

Common Pitfalls

Technical Notes

The {2,} quantifier ensures at least one subdomain prefix exists before the SLD+TLD. Does not enforce TLD validity.