Accounting Format (Negative in Parentheses) Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching accounting format (negative in parentheses), ported and verified for Python. Financial data validation has zero tolerance for false negatives — a missed invalid entry can corrupt downstream calculations. 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

# Accounting Format (Negative in Parentheses)
# ReDoS-safe | RegexVault — Finance > Currency & Money

import re

accounting_format_negative_in_parentheses_pattern = re.compile(r'^(?:\((?:(?:[1-9][0-9]*(?:,[0-9]{3})*)|0)(?:\.[0-9]{1,2})?\)|(?:(?:[1-9][0-9]*(?:,[0-9]{3})*)|0)(?:\.[0-9]{1,2})?)$')

def validate_accounting_format_negative_in_parentheses(value: str) -> bool:
    return bool(accounting_format_negative_in_parentheses_pattern.fullmatch(value))

# Example
print(validate_accounting_format_negative_in_parentheses("1,234.56"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Currency & Money 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

Standard accounting/financial statement format. Parentheses denote debit or loss depending on context. Strip parentheses and negate when converting to numeric type for calculation.