Python Validate International Securities Identification Number

Validate International Securities Identification Number

 https://rosettacode.org/wiki/Validate_International_Securities_Identification_Number#Python

https://rosettacode.org/wiki/Luhn_test_of_credit_card_numbers

https://www.lei-lookup.com/record/?page_nr=4

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I'm working on modernizing Rosetta Code's infrastructure. Starting with communications. Please accept this time-limited open invite to RC's Slack.. --Michael Mol (talk) 20:59, 30 May 2020 (UTC)

Validate International Securities Identification Number

Validate International Securities Identification Number
You are encouraged to solve this task according to the task description, using any language you may know.

An International Securities Identification Number (ISIN) is a unique international identifier for a financial security such as a stock or bond.

Task

Write a function or program that takes a string as input, and checks whether it is a valid ISIN.

It is only valid if it has the correct format,   and   the embedded checksum is correct.

Demonstrate that your code passes the test-cases listed below.

Details

The format of an ISIN is as follows:

┌───────────── a 2-character ISO country code (A-Z)

│ ┌─────────── a 9-character security code (A-Z, 0-9)

│ │        ┌── a checksum digit (0-9)

AU0000XVGZA3

For this task, you may assume that any 2-character alphabetic sequence is a valid country code.

The checksum can be validated as follows:

1. Replace letters with digits, by converting each character from base 36 to base 10, e.g. AU0000XVGZA3 →1030000033311635103.
2. Perform the Luhn test on this base-10 number.
   There is a separate task for this test: Luhn test of credit card numbers.
   You don't have to replicate the implementation of this test here   ───   you can just call the existing function from that task.   (Add a comment stating if you did this.)

Test cases

ISIN	Validity	Comment
US0378331005	valid
US0373831005	not valid	The transposition typo is caught by the checksum constraint.
U50378331005	not valid	The substitution typo is caught by the format constraint.
US03378331005	not valid	The duplication typo is caught by the format constraint.
AU0000XVGZA3	valid
AU0000VXGZA3	valid	Unfortunately, not all transposition typos are caught by the checksum constraint.
FR0000988040	valid

(The comments are just informational.   Your function should simply return a Boolean result.   See #Raku for a reference solution.)

Related task:

• Luhn test of credit card numbers

Also see

• Interactive online ISIN validator
• Wikipedia article: International Securities Identification Number

Python[edit]

def check_isin(a):
    if len(a) != 12 or not all(c.isalpha() for c in a[:2]) or not all(c.isalnum() for c in a[2:]):
        return False
    s = "".join(str(int(c, 36)) for c in a)
    return 0 == (sum(sum(divmod(2 * (ord(c) - 48), 10)) for c in s[-2::-2]) +
                 sum(ord(c) - 48 for c in s[::-2])) % 10
 
# A more readable version 
def check_isin_alt(a):
    if len(a) != 12:
        return False
    s = []
    for i, c in enumerate(a):
        if c.isdigit():
            if i < 2:
                return False
            s.append(ord(c) - 48)
        elif c.isupper():
            if i == 11:
                return False
            s += divmod(ord(c) - 55, 10)
        else:
            return False
    v = sum(s[::-2])
    for k in s[-2::-2]:
        k = 2 * k
        v += k - 9 if k > 9 else k
    return v % 10 == 0
 
[check_isin(s) for s in ["US0378331005", "US0373831005", "U50378331005", "US03378331005",
                         "AU0000XVGZA3", "AU0000VXGZA3", "FR0000988040"]]
 
# [True, False, False, False, True, True, True]