Japanese Date Format (YYYY年MM月DD日) Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching japanese date format (yyyy年mm月dd日), 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 Date Format (YYYY年MM月DD日)
# ReDoS-safe | RegexVault — Localization > Date Formats

import re

japanese_date_format_yyyymmdd_pattern = re.compile(r'^((?:19|20)[0-9]{2})年(0?[1-9]|1[0-2])月(0?[1-9]|[12][0-9]|3[01])日$')

def validate_japanese_date_format_yyyymmdd(value: str) -> bool:
    return bool(japanese_date_format_yyyymmdd_pattern.fullmatch(value))

# Example
print(validate_japanese_date_format_yyyymmdd("2024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

Capture groups: 1=year (western/Gregorian), 2=month, 3=day. Japan also uses its imperial era system (Reiwa/令和, Heiwa/平成, etc.) — those require separate patterns as they reset year numbering.