Port in URL Context (:port) Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching port in url context (:port), 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

# Port in URL Context (:port)
# ReDoS-safe | RegexVault — Web & Network > Port

import re

port_in_url_context_port_pattern = re.compile(r':(?:6553[0-5]|655[0-2][0-9]|65[0-4][0-9]{2}|6[0-4][0-9]{3}|[1-5][0-9]{4}|[1-9][0-9]{0,3})(?=[/?#\s]|$)')

def validate_port_in_url_context_port(value: str) -> bool:
    return bool(port_in_url_context_port_pattern.fullmatch(value))

# Example
print(validate_port_in_url_context_port(":80"))  # 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

The lookahead (?=[/?#\s]|$) ensures the port is not followed by other URL characters that would indicate it is part of a different token. Go requires a separate bounds check.