Cron Day-of-Week Field Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching cron day-of-week field, 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

# Cron Day-of-Week Field
# ReDoS-safe | RegexVault — Dev & Systems > Cron

import re

cron_dayofweek_field_pattern = re.compile(r'^(?:[?]|\*(?:/[1-7])?|[0-7](?:-[0-7](?:/[1-7])?)?(?:,[0-7](?:-[0-7])?)*)$')

def validate_cron_dayofweek_field(value: str) -> bool:
    return bool(cron_dayofweek_field_pattern.fullmatch(value))

# Example
print(validate_cron_dayofweek_field("*"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > Cron 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

Both 0 and 7 represent Sunday in most cron implementations. Quartz uses 1-7 where 1=Sunday. Weekday scheduling: 1-5 for Monday-Friday.