Hex Color Code (#RGB / #RRGGBB / #RRGGBBAA) Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching hex color code (#rgb / #rrggbb / #rrggbbaa), 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

# Hex Color Code (#RGB / #RRGGBB / #RRGGBBAA)
# ReDoS-safe | RegexVault — Web & Network > Misc

import re

hex_color_code_rgb_rrggbb_rrggbbaa_pattern = re.compile(r'^#(?:[0-9a-fA-F]{8}|[0-9a-fA-F]{6}|[0-9a-fA-F]{3})$')

def validate_hex_color_code_rgb_rrggbb_rrggbbaa(value: str) -> bool:
    return bool(hex_color_code_rgb_rrggbb_rrggbbaa_pattern.fullmatch(value))

# Example
print(validate_hex_color_code_rgb_rrggbb_rrggbbaa("#fff"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Misc 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 alternation order matters: 8-digit first, then 6, then 3 — prevents 6-char strings from partially matching the 3-char alternative. CSS4 also supports 4-digit (#RGBA) — add [0-9a-fA-F]{4} to support it.