URL Query Parameter (Single key=value) Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching url query parameter (single key=value), 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

# URL Query Parameter (Single key=value)
# ReDoS-safe | RegexVault — Web & Network > URL

import re

url_query_parameter_single_keyvalue_pattern = re.compile(r'(?:^|[?&])([a-zA-Z][a-zA-Z0-9_\-.]{0,99})=([^&\s#]*)')

def validate_url_query_parameter_single_keyvalue(value: str) -> bool:
    return bool(url_query_parameter_single_keyvalue_pattern.fullmatch(value))

# Example
print(validate_url_query_parameter_single_keyvalue("?key=value"))  # 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

Use with the g flag in JS to iterate all parameters. Capture group 1 is the key, group 2 is the raw value. URL-decode values before use: decodeURIComponent(value.replace(/\+/g, ' ')).