Invoice Number Regex for Python

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching invoice number, 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

# Invoice Number
# ReDoS-safe | RegexVault — Finance > Financial Formats

import re

invoice_number_pattern = re.compile(r'^[A-Z0-9\-]{4,15}$')

def validate_invoice_number(value: str) -> bool:
    return bool(invoice_number_pattern.fullmatch(value))

# Example
print(validate_invoice_number("INV-00001"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Financial Formats 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

Invoice numbering conventions vary widely. This pattern covers the most common formats. The prefix identifies the document type (INV, SINV, PO, CN for credit note). Pad with leading zeros for sortability.