Relative URL Path Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching relative url path, 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

# Relative URL Path
# ReDoS-safe | RegexVault — Web & Network > URL

import re

relative_url_path_pattern = re.compile(r'^(?!//)(?:/[a-zA-Z0-9\-._~!$&'()*+,;=:@%]*)+(?:\?[^#\s]*)?(?:#[^\s]*)?$')

def validate_relative_url_path(value: str) -> bool:
    return bool(relative_url_path_pattern.fullmatch(value))

# Example
print(validate_relative_url_path("/"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Web & Network > URL 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

Relative paths must start with / (absolute path reference). Protocol-relative URLs (//example.com) are intentionally excluded — use net-url-01 for those.