INI File Key=Value Pair Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching ini file key=value pair, 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

# INI File Key=Value Pair
# ReDoS-safe | RegexVault — Dev & Systems > Config

import re

ini_file_keyvalue_pair_pattern = re.compile(r'^([a-zA-Z_][a-zA-Z0-9_.\-]{0,254})\s*[=:]\s*([^;#\n]*)\s*(?:[;#].*)?$')

def validate_ini_file_keyvalue_pair(value: str) -> bool:
    return bool(ini_file_keyvalue_pair_pattern.fullmatch(value))

# Example
print(validate_ini_file_keyvalue_pair("host=localhost"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Dev & Systems > Config 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

Groups: 1=key, 2=value (trailing whitespace and inline comment stripped). Both = and : are valid delimiters (Python configparser accepts both). git config uses = only.