Step by Step solution about How to resolve the algorithm IBAN step by step in the Python programming language

This piece of code provides a function to validate an IBAN (International Bank Account Number). It's a string made up of alphanumeric characters, typically used for international money transfers. The function checks the length and structure of the IBAN against a dictionary of expected lengths for different country codes.

It follows these steps to check if the IBAN is valid:

1. Removes any spaces or tabs from the input string.

2. Verifies that the string contains only alphanumeric characters (ie. [A-Z0-9])

3. Checks if the length of the string matches the expected length for the country code specified in the first two characters of the IBAN using a dictionary _country2length.

4. Shifts the string by four characters and concatenates the first four characters to the end of the string.

5. Converts each character in the string to a base-36 integer (0-35), representing digits 0-9 and letters A-Z.

6. Performs a modulo 97 operation on the resulting integer, checking if the remainder is equal to 1.

If all these conditions are met, the IBAN is considered valid, and the function returns True; otherwise, it returns False.

In the main function, two sample IBANs are provided for testing:

• GB82 WEST 1234 5698 7654 32 is an actual valid IBAN for a UK bank account.

• GB82 TEST 1234 5698 7654 32 is an invalid IBAN as it does not match the correct format for a UK IBAN.

When you run the code, it will output the validation results for each of the sample IBANs, indicating whether they are valid or not.

import re

_country2length = dict(
    AL=28, AD=24, AT=20, AZ=28, BE=16, BH=22, BA=20, BR=29,
    BG=22, CR=21, HR=21, CY=28, CZ=24, DK=18, DO=28, EE=20,
    FO=18, FI=18, FR=27, GE=22, DE=22, GI=23, GR=27, GL=18,
    GT=28, HU=28, IS=26, IE=22, IL=23, IT=27, KZ=20, KW=30,
    LV=21, LB=28, LI=21, LT=20, LU=20, MK=19, MT=31, MR=27,
    MU=30, MC=27, MD=24, ME=22, NL=18, NO=15, PK=24, PS=29,
    PL=28, PT=25, RO=24, SM=27, SA=24, RS=22, SK=24, SI=19,
    ES=24, SE=24, CH=21, TN=24, TR=26, AE=23, GB=22, VG=24 )

def valid_iban(iban):
    # Ensure upper alphanumeric input.
    iban = iban.replace(' ','').replace('\t','')
    if not re.match(r'^[\dA-Z]+$', iban): 
        return False
    # Validate country code against expected length.
    if len(iban) != _country2length[iban[:2]]:
        return False
    # Shift and convert.
    iban = iban[4:] + iban[:4]
    digits = int(''.join(str(int(ch, 36)) for ch in iban)) #BASE 36: 0..9,A..Z -> 0..35
    return digits % 97 == 1

if __name__ == '__main__':
    for account in ["GB82 WEST 1234 5698 7654 32", "GB82 TEST 1234 5698 7654 32"]:
        print('%s validation is: %s' % (account, valid_iban(account)))