def validate_brand(card_number: str) -> PaymentCardBrand:
        """Validate length based on BIN for major brands:
        https://en.wikipedia.org/wiki/Payment_card_number#Issuer_identification_number_(IIN).
        """
        if card_number[0] == '4':
            brand = PaymentCardBrand.visa
        elif 51 <= int(card_number[:2]) <= 55:
            brand = PaymentCardBrand.mastercard
        elif card_number[:2] in {'34', '37'}:
            brand = PaymentCardBrand.amex
        else:
            brand = PaymentCardBrand.other

        required_length: None | int | str = None
        if brand in PaymentCardBrand.mastercard:
            required_length = 16
            valid = len(card_number) == required_length
        elif brand == PaymentCardBrand.visa:
            required_length = '13, 16 or 19'
            valid = len(card_number) in {13, 16, 19}
        elif brand == PaymentCardBrand.amex:
            required_length = 15
            valid = len(card_number) == required_length
        else:
            valid = True

        if not valid:
            raise PydanticCustomError(
                'payment_card_number_brand',
                'Length for a {brand} card must be {required_length}',
                {'brand': brand, 'required_length': required_length},
            )
        return brand
Validate length based on BIN for major brands:
        https://en.wikipedia.org/wiki/Payment_card_number#Issuer_identification_number_(IIN).
        
pydantic/types.py