ISO 8601 Ordinal Date (YYYY-DDD) Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching iso 8601 ordinal date (yyyy-ddd), 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

# ISO 8601 Ordinal Date (YYYY-DDD)
# ReDoS-safe | RegexVault — Localization > Date Formats

import re

iso_8601_ordinal_date_yyyyddd_pattern = re.compile(r'^((?:19|20)[0-9]{2})-(00[1-9]|0[1-9][0-9]|[12][0-9]{2}|3[0-5][0-9]|36[0-6])$')

def validate_iso_8601_ordinal_date_yyyyddd(value: str) -> bool:
    return bool(iso_8601_ordinal_date_yyyyddd_pattern.fullmatch(value))

# Example
print(validate_iso_8601_ordinal_date_yyyyddd("2024-001"))  # 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

Day 001 = January 1, day 365 = December 31 (non-leap), day 366 is only valid in leap years. Used in DOY-based systems, scientific datasets, and some military applications. Convert to calendar date with date library.