American Express Card Number Regex for Python

What this pattern does

This page provides a lightweight, single-purpose regular expression for matching american express card 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

# American Express Card Number
# ReDoS-safe | RegexVault — Finance > Card Numbers

import re

american_express_card_number_pattern = re.compile(r'^3[47][0-9]{13}$')

def validate_american_express_card_number(value: str) -> bool:
    return bool(american_express_card_number_pattern.fullmatch(value))

# Example
print(validate_american_express_card_number("378282246310005"))  # True

Test Cases

When to use this pattern

This pattern is drawn from the Finance > Card Numbers 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

Amex uses 15-digit card numbers (unlike 16-digit Visa/Mastercard). CVV is 4 digits on the front (not 3 on the back). Amex uses different group format for display: 4-6-5.