24-Hour Time with Seconds (HH:MM:SS) Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching 24-hour time with seconds (hh:mm:ss), 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

# 24-Hour Time with Seconds (HH:MM:SS)
# ReDoS-safe | RegexVault — Localization > Time Formats

import re

24hour_time_with_seconds_hhmmss_pattern = re.compile(r'^(2[0-3]|[01][0-9]):([0-5][0-9]):([0-5][0-9])$')

def validate_24hour_time_with_seconds_hhmmss(value: str) -> bool:
    return bool(24hour_time_with_seconds_hhmmss_pattern.fullmatch(value))

# Example
print(validate_24hour_time_with_seconds_hhmmss("00:00:00"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Localization > Time Formats 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

Requires zero-padded hours (09, not 9). Does not include fractional seconds. For sub-second precision, see loc-time-03. Note: 23:59:60 would be a leap second — technically valid in UTC but rare.