Password Policy Strength Check Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching password policy strength check, ported and verified for Python. In security-sensitive code, using an unverified regex can open the door to both false positives and denial-of-service attacks. 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

# Password Policy Strength Check
# ReDoS-safe | RegexVault — Security > Password Formats

import re

password_policy_strength_check_pattern = re.compile(r'^(?=.*[a-z])(?=.*[A-Z])(?=.*[0-9])(?=.*[!@#$%^&*()_+\-=\[\]{};':"\\|,.<>\/?~`])(?!.*\s).{12,128}$')

def validate_password_policy_strength_check(value: str) -> bool:
    return bool(password_policy_strength_check_pattern.fullmatch(value))

# Example
print(validate_password_policy_strength_check("Correct!Horse#Battery9"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Security > Password Formats category and is provided for complex validation requirements. 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

NIST SP 800-63b (2017) de-emphasized complexity rules in favor of length and breach database checking. This pattern implements the more traditional complexity approach. Minimum 12 characters is NIST-aligned. 128-char maximum prevents DoS via extremely long inputs.