Well-Known Port (1–1023) Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching well-known port (1–1023), 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

# Well-Known Port (1–1023)
# ReDoS-safe | RegexVault — Web & Network > Port

import re

wellknown_port_11023_pattern = re.compile(r'^(?:102[0-3]|10[01][0-9]|[1-9][0-9]{0,2})$')

def validate_wellknown_port_11023(value: str) -> bool:
    return bool(wellknown_port_11023_pattern.fullmatch(value))

# Example
print(validate_wellknown_port_11023("1"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > Port 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

Common well-known ports: 21 (FTP), 22 (SSH), 25 (SMTP), 53 (DNS), 80 (HTTP), 443 (HTTPS). Full list maintained by IANA.