Japanese Imperial Era Year (Reiwa/Heisei/Showa) Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching japanese imperial era year (reiwa/heisei/showa), 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

# Japanese Imperial Era Year (Reiwa/Heisei/Showa)
# ReDoS-safe | RegexVault — Localization > Date Formats

import re

japanese_imperial_era_year_reiwaheiseishowa_pattern = re.compile(r'^(?:(令和|R)((?:[1-9]|[1-9][0-9]))|(平成|H)((?:[1-9]|[12][0-9]|3[01]))|(昭和|S)((?:[1-9]|[12][0-9]|3[0-9]|6[0-4])))年(0?[1-9]|1[0-2])月(0?[1-9]|[12][0-9]|3[01])日$')

def validate_japanese_imperial_era_year_reiwaheiseishowa(value: str) -> bool:
    return bool(japanese_imperial_era_year_reiwaheiseishowa_pattern.fullmatch(value))

# Example
print(validate_japanese_imperial_era_year_reiwaheiseishowa("令和6年1月15日"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Localization > Date 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

Era limits: 令和/Reiwa started May 1, 2019 (max year currently ~6). 平成/Heisei: 1-31 (1989-2019). 昭和/Showa: 1-64 (1926-1989). Meiji and Taisho are pre-1926 and excluded here. Convert to Gregorian for storage.