IPv6 Loopback Address Regex for Python

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching ipv6 loopback address, 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

# IPv6 Loopback Address
# ReDoS-safe | RegexVault — Web & Network > IPv6

import re

ipv6_loopback_address_pattern = re.compile(r'^(?:::1|(?:0{1,4}:){7}0*1)$')

def validate_ipv6_loopback_address(value: str) -> bool:
    return bool(ipv6_loopback_address_pattern.fullmatch(value))

# Example
print(validate_ipv6_loopback_address("::1"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > IPv6 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

Prefer ::1 normalization in storage. The pattern accepts expanded forms for input validation but ::1 is the canonical representation per RFC 5952.