ISO 8601 Week Date (YYYY-Www-D) Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching iso 8601 week date (yyyy-www-d), 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 Week Date (YYYY-Www-D)
# ReDoS-safe | RegexVault — Localization > Date Formats

import re

iso_8601_week_date_yyyywwwd_pattern = re.compile(r'^((?:19|20)[0-9]{2})-W(0[1-9]|[1-4][0-9]|5[0-3])(?:-([1-7]))?$')

def validate_iso_8601_week_date_yyyywwwd(value: str) -> bool:
    return bool(iso_8601_week_date_yyyywwwd_pattern.fullmatch(value))

# Example
print(validate_iso_8601_week_date_yyyywwwd("2024-W03"))  # 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

ISO week year may differ from calendar year — the first week of the year contains the first Thursday. Week 1 starts from Monday. Day: 1=Monday, 7=Sunday. Some years have 53 weeks (ISO 8601 long years).