Validate ISIN Format | Dataford Interview Questions

BlackRock's Aladdin platform processes securities identified by ISINs. Write a function that validates whether a string has the required ISIN structure.

A valid ISIN must contain exactly 12 characters:

Characters at positions 0 and 1 must be uppercase ASCII letters representing the country code.
Characters at positions 2 through 10 must be ASCII letters or digits.
Character at position 11 must be an ASCII digit representing the check digit.

This task validates the required format only. You do not need to calculate or verify the mathematical ISIN check-digit algorithm.

Formal Specification

Given a string isin, return True if it satisfies all rules above, and return False otherwise. The input is a Python string, and the output must be a Boolean.

Constraints

0 <= len(isin) <= 10^5
The input is a Python string
The format is case-sensitive
Only the structure is validated, not the mathematical ISIN check-digit algorithm

Function Signature

def is_valid_isin(isin):

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