Task: IBAN
C#:     public class IbanValidator : IValidateTypes
    {
        public ValidationResult Validate(string value)
        {
            
            if (string.IsNullOrEmpty(value))
                return ValidationResult.ValueMissing;

            if (value.Length < 2)
                return ValidationResult.ValueTooSmall;

            var countryCode = value.Substring(0, 2).ToUpper();

            int lengthForCountryCode;

            var countryCodeKnown = Lengths.TryGetValue(countryCode, out lengthForCountryCode);
            if (!countryCodeKnown)
            {
                return ValidationResult.CountryCodeNotKnown;
            }

            
            if (value.Length < lengthForCountryCode)
                return ValidationResult.ValueTooSmall;

            if (value.Length > lengthForCountryCode)
                return ValidationResult.ValueTooBig;

            value = value.ToUpper();
            var newIban = value.Substring(4) + value.Substring(0, 4);

            newIban = Regex.Replace(newIban, @"\D", match => (match.Value[0] - 55).ToString());

            var remainder = BigInteger.Parse(newIban) % 97;

            if (remainder != 1)
                return ValidationResult.ValueFailsModule97Check;

            return ValidationResult.IsValid;
        }

        public enum ValidationResult
        {
            IsValid,
            ValueMissing,
            ValueTooSmall,
            ValueTooBig,
            ValueFailsModule97Check,
            CountryCodeNotKnown
        }

        private static readonly IDictionary<string, int> Lengths = new Dictionary<string, int>
        {
            {"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}
        };
    }

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)))