ISIN (International Securities Identification Number) Regex for Python

What this pattern does

This page provides a comprehensive, battle-tested regular expression for matching isin (international securities identification 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

# ISIN (International Securities Identification Number)
# ReDoS-safe | RegexVault — Finance > Securities & Trading

import re

isin_international_securities_identification_number_pattern = re.compile(r'^(?!XX)[A-Z]{2}[A-Z0-9]{9}[0-9]$')

def validate_isin_international_securities_identification_number(value: str) -> bool:
    return bool(isin_international_securities_identification_number_pattern.fullmatch(value))

# Example
print(validate_isin_international_securities_identification_number("US0378331005"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Securities & Trading 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

ISIN structure: 2-char ISO 3166-1 country code + 9-char NSIN (National Securities Identifying Number, right-padded with zeros) + 1 Luhn check digit. US ISINs use CUSIP as the NSIN.