12-Hour Time (H:MM AM/PM) Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching 12-hour time (h:mm am/pm), 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

# 12-Hour Time (H:MM AM/PM)
# ReDoS-safe | RegexVault — Localization > Time Formats

import re

12hour_time_hmm_ampm_pattern = re.compile(r'^(1[0-2]|0?[1-9]):([0-5][0-9])(?::([0-5][0-9]))?\s?(AM|PM|am|pm|Am|Pm)$')

def validate_12hour_time_hmm_ampm(value: str) -> bool:
    return bool(12hour_time_hmm_ampm_pattern.fullmatch(value))

# Example
print(validate_12hour_time_hmm_ampm("12:30 PM"))  # 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

12:00 AM = midnight, 12:00 PM = noon — the most commonly confused values. 12-hour format is standard in US, UK, Australia, and parts of Asia. Many others use 24-hour exclusively.