'Returns 14 character Polish National Business Registry Number,
local entity number.
https://pl.wikipedia.org/wiki/REGON'

@classmethod
def local_regon(cls):

    regon_digits = [int(digit) for digit in list(cls.regon())]
    for _ in range(4):
        regon_digits.append(cls.random_digit())
    regon_digits.append(local_regon_checksum(regon_digits))
    return ''.join((str(digit) for digit in regon_digits))
