Task: IBAN
C++: #include <string>
#include <iostream>
#include <boost/algorithm/string.hpp>
#include <map>
#include <algorithm>
#include <cctype>

using namespace boost::algorithm;

bool isValid(const std::string &ibanstring) {
    static std::map<std::string, int> countrycodes {
        {"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 }
    };
    std::string teststring(ibanstring);
    erase_all(teststring, " "); 
    if (countrycodes.find(teststring.substr(0, 2)) == countrycodes.end())
        return false;
    if (teststring.length() != countrycodes[teststring.substr(0, 2)])
        return false;
    if (!all(teststring, is_alnum()))
        return false;
    to_upper(teststring);
    std::rotate(teststring.begin(), teststring.begin() + 4, teststring.end());

    std::string numberstring; 
    for (const auto &c : teststring) {
        if (std::isdigit(c))
            numberstring += c;
        if (std::isupper(c))
            numberstring += std::to_string(static_cast<int>(c) - 55);
    }
    
    
    
    int segstart = 0;
    int step = 9;
    std::string prepended;
    long number = 0;
    while (segstart < numberstring.length() - step) {
        number = std::stol(prepended + numberstring.substr(segstart, step));
        int remainder = number % 97;
        prepended = std::to_string(remainder);
        if (remainder < 10)
            prepended = "0" + prepended;
        segstart = segstart + step;
        step = 7;
    }
    number = std::stol(prepended + numberstring.substr(segstart));
    return (number % 97 == 1);
}

void SayValidity(const std::string &iban) {
    std::cout << iban << (isValid(iban) ? " is " : " is not ") << "valid\n";
}

int main() {
    SayValidity("GB82 WEST 1234 5698 7654 32");
    SayValidity("GB82TEST12345698765432");
    return 0;
}

Python: 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):
    
    iban = iban.replace(' ','').replace('\t','')
    if not re.match(r'^[\dA-Z]+$', iban): 
        return False
    
    if len(iban) != _country2length[iban[:2]]:
        return False
    
    iban = iban[4:] + iban[:4]
    digits = int(''.join(str(int(ch, 36)) for ch in iban)) 
    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)))