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Picked up from old thread but currently applicable (the IBAN number became more widely required actually this year in Finland). The style was quite alien for modern Python coders, so I massaged the code to my own liking. I removed many temporary variables, as for my opinion they did not make things cleared, and I reformed map lambdas to generators.

# Utility to check the integrity of an IBAN bank account No.
# based on old code in thread:
# Dictionaries - Refer to ISO 7064 mod 97-10 
letter_dic={"A":10, "B":11, "C":12, "D":13, "E":14, "F":15, "G":16, "H":17, "I":18, "J":19, "K":20, "L":21, "M":22,
            "N":23, "O":24, "P":25, "Q":26, "R":27, "S":28, "T":29, "U":30, "V":31, "W":32, "X":33, "Y":34, "Z":35,

# ISO 3166-1 alpha-2 country code
             "CZ":[24,"Czech Republic"],
             "FO":[18,"Faroe Islands"],
             "NO":[15,"Northern Ireland"],
             "SM":[27,"San Marino"],
             "SA":[24,"Saudi Arabia"],
             "GB":[22,"United Kingdom"]}

def check(orig):
    block = 4
    # remove spaces from formatted 
    IBAN = ''.join(c for c in orig if c.isalnum())
    IBAN = IBAN[4:] + IBAN[:4]
    country = IBAN[-4:-2]
    if country not in country_dic:
        raise ValueError('Unknown IBAN country %s' % country)

    length_c, name_c = country_dic[country]

    if len(IBAN) != length_c:
        diff = len(IBAN) - length_c
        raise ValueError('Wrong IBAN length by %s: %s' % (('short by %i' % -diff) if diff < 0 else
                                                          ('too long by %i' % diff), orig))
    elif int("".join(str(letter_dic[x]) for x in IBAN)) % 97 != 1:
        raise ValueError('Incorrect IBAN number: %s' % orig)
        # Accepted: 
        # move IBAN to original order
        IBAN = IBAN[-4:] + IBAN[:-4]
        # return formatted number with spaces
        return ' '.join(IBAN[f:f+block] for f in range(0, len(IBAN), block))

if __name__ == '__main__':
    # Sample IBAN account numbers.
    for  IBAN in ("GB35MIDL40253432144670", "BE31435411161155", "CH5108686001256515001", raw_input("Enter account No. : ").upper()):
            formatted = check(IBAN)
        except ValueError as e:
            print("IBAN account No. accepted.")
            print("Formated bank account No : %s\n" % formatted)

IT/Science/Contracts/Religious translation/interpreting FIN-ENG-FIN
Python programming

Of course there is more consise way of doing the first line, but it does not really matter:

letter_dic= dict((letter, ind) for ind, letter in enumerate("0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ"))
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