IBAN Checker and Generator

iban_checker.py

#!/usr/bin/env python3
"""
Checks for the validity of an IBAN number

You can either pipe IBANS into it, provide it a file directly,
or provide it a single IBAN. In the case of a single IBAN, it'll
show you the steps to verify it.

Samuel Prevost 2021-03-19
"""

import sys
from sys import argv

def main():
    """Main function"""
    if len(argv) == 2 and "-h" in argv[1].lower():
        print(f"Usage: python {argv[0]} (IBAN | -f iban_list.txt | -f -)")
        print("Example:")
        print(f"python {argv[0]} FR76 3000 6000 0112 3456 7890 189")
        print(f"python {argv[0]} -f iban_list.txt")
        print(f"cat iban_list.txt | python {argv[0]}")
        exit(1)

    if len(argv) == 1 or argv[1] == "-f":
        iterator = None
        if len(argv) == 1 or (len(argv) == 3 and argv[2] == "-"):
            iterator = iter(sys.stdin)
        else:
            f = open(argv[2], 'r')
            iterator = iter(f)

        all_good = True

        try:
            for i, line in enumerate(iterator):
                line = line.replace("\n", "")
                if len(line) == 0:
                    continue
                if not check_iban(line, verbose=False):
                    print(f"Line {i+1}: Found invalid IBAN: {line}", file=sys.stderr)
                    all_good = False

            if all_good:
                print("All IBAN were valid", file=sys.stderr)

        except KeyboardInterrupt:
            sys.stdout.flush()

        finally:
            if hasattr(iterator, "close") and callable(iterator.close):
                iterator.close()

    else:
        iban = ''.join(argv[1:])
        if check_iban(iban):
            print("Valid IBAN")
        else:
            print("Invalid IBAN")
            exit(1)

    print("Done.", file=sys.stderr)

def check_iban(iban, verbose=True):
    iban = iban.replace(' ', '').upper()
    if verbose: print("IBAN :\t\t\t", iban)
    iban = iban[4:] + iban[:4]
    if verbose: print("IBAN rearranged: \t", iban)
    iban_int = ""
    for c in iban:
        if ord("A") <= ord(c) <= ord("Z"):
            # A=10, B=11, ..., Z=35 that's why letters count double, 
            # because they're encoded on two decimal digits
            iban_int += str(ord(c)-55)
        else:
            iban_int += c
    if verbose: print("IBAN in int: \t\t", iban_int)

    iban_int = int(iban_int)

    if verbose: print("Mod 97: \t\t", iban_int % 97)
    return iban_int % 97 == 1

if __name__ == "__main__":
    main()

iban_generator.py

#!/usr/bin/env python3
"""
Generates valid IBAN numbers that (possibly) don't exist
For now it only works with French (FR) IBAN
To add your country, just find out the length of your 
BBAN by counting the number of digits after the first
four chars. Letters in that BBAN part count for two chars.

Samuel Prevost 2021-03-19
"""

from sys import argv
import numpy as np

def main():
    """Main function"""

    if len(argv) != 3:
        print(f"Usage: python3 {argv[0]} COUNTRY IBAN_COUNT")
        exit(1)

    # IBAN:
    # FR896537193277159353833949
    #     ^^^^^^^^^^^^^^^^^^^^^^
    #      Basic Bank Acc Num (BBAN)

    bban_sizes = {
        "FR": 23
    }
    country = argv[1]

    if country not in bban_sizes.keys():
        print("Country not yet supported !")
        print("Possible countries:")
        print(", ".join(bban_sizes.keys()))
        exit(1)

    country_code = get_country_code(country)
    for _ in range(int(argv[2])):
        while True:
            try:
                r = list(np.random.randint(0, 10, size=bban_sizes[country]))
                r += [country_code]
                r = int("".join(str(n) for n in r))

                check_digits = bruteforce_check_digit(r)
                iban_int = add_num(r, check_digits)
                iban = to_string_iban(iban_int)
                print(iban)
                break
            except CheckDigitsError:
                continue


class CheckDigitsError(ValueError):
    pass

def bruteforce_check_digit(r):
    for i in range(10, 100):
        iban_int = add_num(r, i)
        if iban_int % 97 == 1:
            return i
    raise CheckDigitsError("Didn't find suitable check digit !")

def add_num(a,b):
    return int(str(a) + str(b))

def get_country_code(country_letters):
    # FR -> 1527
    return int("".join([str(ord(c)-55) for c in country_letters]))

def to_string_iban(int_iban):
    str_iban = str(int_iban)
    str_iban = str_iban[-6:] + str_iban[:-6]
    str_iban = chr(int(str_iban[:2])+55) + chr(int(str_iban[2:4])+55) + str_iban[4:]
    return str_iban

if __name__ == "__main__":
    main()