Syslog Priority and Facility Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching syslog priority and facility, 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

# Syslog Priority and Facility
# ReDoS-safe | RegexVault — Dev & Systems > Log Parsing

import re

syslog_priority_and_facility_pattern = re.compile(r'^<((?:19[01]|1[0-8][0-9]|[1-9][0-9]|[0-9]))>')

def validate_syslog_priority_and_facility(value: str) -> bool:
    return bool(syslog_priority_and_facility_pattern.fullmatch(value))

# Example
print(validate_syslog_priority_and_facility("<0>message"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > Log Parsing 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

Priority = facility * 8 + severity. Facility: 0=kernel, 1=user, 3=daemon, 4=auth, 16-23=local0-7. Severity: 0=emergency, 1=alert, 2=critical, 3=error, 4=warning, 5=notice, 6=info, 7=debug. Valid range 0-191.