IPv6 Full (Expanded + Compressed) Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching ipv6 full (expanded + compressed), 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 Full (Expanded + Compressed)
# ReDoS-safe | RegexVault — Web & Network > IPv6

import re

ipv6_full_expanded_compressed_pattern = re.compile(r'^(([0-9a-fA-F]{1,4}:){7}[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}:){1,7}:|([0-9a-fA-F]{1,4}:){1,6}:[0-9a-fA-F]{1,4}|([0-9a-fA-F]{1,4}:){1,5}(:[0-9a-fA-F]{1,4}){1,2}|([0-9a-fA-F]{1,4}:){1,4}(:[0-9a-fA-F]{1,4}){1,3}|([0-9a-fA-F]{1,4}:){1,3}(:[0-9a-fA-F]{1,4}){1,4}|([0-9a-fA-F]{1,4}:){1,2}(:[0-9a-fA-F]{1,4}){1,5}|[0-9a-fA-F]{1,4}:(:[0-9a-fA-F]{1,4}){1,6}|:(:[0-9a-fA-F]{1,4}){1,7}|::)$')

def validate_ipv6_full_expanded_compressed(value: str) -> bool:
    return bool(ipv6_full_expanded_compressed_pattern.fullmatch(value))

# Example
print(validate_ipv6_full_expanded_compressed("2001:db8::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

Each alternation handles a specific number of groups before/after ::. The :: can appear at most once (enforced by alternation structure, not lookahead). Go's RE2 may have issues with alternation of this complexity — use net.ParseIP() in Go instead.