Dutch IBAN generator

iban.py

"""
Python 3 Generator for Dutch IBANs.
Should be equivalent to gist.github.com/martijnluinstra/9ca0f62b9ddc01288be8a6072d29b029
Demo: projects.martijnluinstra.nl/iban/

Copyright (c) 2017 Martijn Luinstra
"""

import functools
import operator


def iban_to_number(iban):
    """ Converts IBAN to the decimal representation as used for validation """
    code = iban[4:] + iban[:4]
    def generate(code):
        for x in code:
            try:
                yield str(int(x))
            except:
                yield str(ord(x) - 55)
    return int(''.join(generate(code.upper())))


def validate_iban(iban):
    """ Validates IBAN based on checksum """
    return iban_to_number(iban) % 97 == 1


def generate_account_number(unchecked):
    """ Generates elfproef-valid account number with based on numberic string """
    length = len(unchecked) + 1
    total = sum(int(x) * (length - idx) for idx, x in enumerate(unchecked))
    check = 11 - (total % 11)
    if check > 0 and check < 10:
        return unchecked + str(check)
    # Did not find a number that passes the elfproef, increase unchecked and try again
    return generate_account_number(str(int(unchecked) + 1))


def generate_iban(seed, bank_code=None, country='NL', account_length=9):
    """ Generates realistic Dutch IBAN based on seed and (list of) bank code(s) """
    codes = (ord(x) for x in seed.upper())
    number = 1
    for idx, x in enumerate(codes):
        number *= x + idx
    number = str(number).strip('0')

    account = generate_account_number(number[:account_length-1])
    account = '{:0>{}}'.format(account, account_length + 1)

    if not bank_code:
        bank_code = 'BANK'
    elif isinstance(bank_code, list):
        idx = (ord(number[0]) * ord(number[-1])) % len(bank_code)
        bank_code = bank_code[idx]

    remainder = iban_to_number(''.join((country, '00', bank_code, account))) % 97
    check = '{:0>2}'.format(98 - remainder)

    return ''.join((country, check, bank_code, account))