Validate User IDs in Python | Dataford Interview Questions

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Problem

Moovit data pipelines receive user IDs as strings. Validate whether an ID follows the required format and contains a correct checksum.

A valid ID must have the exact structure MVT-MARKET-BODY-CHECK, where:

MVT is the literal prefix.
MARKET contains 2 to 4 uppercase ASCII letters.
BODY contains 6 to 12 ASCII digits.
CHECK contains exactly one ASCII digit.
The check digit is the Luhn check digit for BODY. To calculate it, scan BODY from right to left, double digits at positions 0, 2, 4, and so on, subtract 9 when a doubled value exceeds 9, then choose the digit that makes the total divisible by 10.

Implement is_valid_user_id(user_id) and return True only when every rule is satisfied. Return False for malformed input, incorrect casing, invalid characters, or an incorrect checksum.

Constraints

1 <= len(user_id) <= 30
The identifier uses exactly three hyphens
MARKET contains 2 to 4 uppercase ASCII letters
BODY contains 6 to 12 ASCII digits
CHECK contains exactly one ASCII digit
No leading or trailing whitespace is allowed

Function Signature

def is_valid_user_id(user_id):