Returns 14 character Polish National Business Registry Number,
        local entity number.

        https://pl.wikipedia.org/wiki/REGON

def local_regon(self):
        """
        Returns 14 character Polish National Business Registry Number,
        local entity number.

        https://pl.wikipedia.org/wiki/REGON
        """
        regon_digits = [int(digit) for digit in list(self.regon())]

        for _ in range(4):
            regon_digits.append(self.random_digit())

        regon_digits.append(local_regon_checksum(regon_digits))

        return ''.join(str(digit) for digit in regon_digits)