validators.py

class ValueCleaner(object):
    def __call__(self, value):
        """Returns the value that is cleaned for database usage"""
        return value

    def display_value(self, value):
        """Returns the value that can be used for display"""
        return self(value)


class UpperCaseValueCleaner(ValueCleaner):
    def __call__(self, value):
        """Returns the value that is cleaned for database usage"""
        if value is not None:
            return value.upper().replace(' ', '').replace('-', '').replace('.', '')
        return value


def _get_check_digit(to_check, factors, mod=11):
    """Method that calculates a check digit based on the following formula:

    (10x_1+9x_2+8x_3+7x_4+6x_5+5x_6+4x_7+3x_8+2x_9+x_10) mod [mod]
    where x_1 thru x_10 are values from to_check
    and 10..1 are values from factors

    Also known as the elfproef
    """
    return sum(int(to_check[i]) * factors[i] for i in range(len(factors))) % mod


def _get_mod97_value(to_check, characters=None, mod=97):
    """Method that calculates a check digit based on the formula used for the mod97
    check digit method. This method replaces all non-numeric values in the string with
    two digits (i.e. A=10, B=11, etc) and then calculates a modulus of this value.
    """
    digits = ""
    for character in to_check:
        if characters and character in characters:
            digits += characters
        elif character.isdigit():
            digits += character
        elif character.isalpha() and character.isupper():
            digits += str(ord(character) - ord('A') + 10)
        else:
            raise ValueError("not a valid character: %s" % character)

    return int(digits) % mod