Decimal Monetary Amount Regex for Python

What this pattern does

This page provides a well-structured, multi-part regular expression for matching decimal monetary amount, 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

# Decimal Monetary Amount
# ReDoS-safe | RegexVault — Finance > Currency & Money

import re

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

def validate_decimal_monetary_amount(value: str) -> bool:
    return bool(decimal_monetary_amount_pattern.fullmatch(value))

# Example
print(validate_decimal_monetary_amount("0"))  # 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

Enforces comma grouping (1,234 not 1234 with thousands). Strip commas before parsing to float. Allows negative amounts. For amounts without thousand separators, use: ^-?[0-9]+(?:\.[0-9]{1,2})?$