FA-72771 / Check-digit algorithms / Open access

LEI check digits lose the leading zero · case 01

Check values below 10 produce a 19-character LEI.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The check is appended with str(), dropping the leading zero.

THE FAILURE

The check is appended with str(), dropping the leading zero.

Unsuccessful approach: Space padding keeps the length but inserts an invalid character.

Case contract

Generate ISO 17442 LEI check digits (ISO 7064 MOD 97-10): the 18-character alphanumeric prefix is upper-cased (other input returns None), "00" is appended, letters become 10..35, and the check is 98 - (number mod 97) written as exactly two digits. Return the 20-character LEI.

Why this case matters

Regulatory reporting tools assign and verify legal entity identifiers.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(prefix):
    t = prefix.upper()
    if len(t) != 18 or not t.isascii() or not t.isalnum():
        return None
    n = int(''.join(str(int(ch, 36)) for ch in t + '00'))
    return t + str(98 - n % 97)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression ["TD7FDXWKLVRV07ALBK"]', ['TD7FDXWKLVRV07ALBK'], 'TD7FDXWKLVRV07ALBK05'], ['regression ["64WI551TBNLAZEBU15"]', ['64WI551TBNLAZEBU15'], '64WI551TBNLAZEBU1502'], ['control ["NH4O4Q9HMI8RUJ0D6Y"]', ['NH4O4Q9HMI8RUJ0D6Y'], 'NH4O4Q9HMI8RUJ0D6Y73'], ['control ["9K6IWOG7TS4VC3SHAM"]', ['9K6IWOG7TS4VC3SHAM'], '9K6IWOG7TS4VC3SHAM78'], ['control ["HTJBP9O1O9QSYUUD3R"]', ['HTJBP9O1O9QSYUUD3R'], 'HTJBP9O1O9QSYUUD3R38'], ['control ["ACLPCCV3EGBW4QG3I6"]', ['ACLPCCV3EGBW4QG3I6'], 'ACLPCCV3EGBW4QG3I685'], ['control ["II5XCIYZ03SDPPSQ7Z"]', ['II5XCIYZ03SDPPSQ7Z'], 'II5XCIYZ03SDPPSQ7Z30'], ['control ["H6UNZ3Z93AZ7BYYPJC"]', ['H6UNZ3Z93AZ7BYYPJC'], 'H6UNZ3Z93AZ7BYYPJC84']], [['regression ["64WI551TBNLAZEBU15"]', ['64WI551TBNLAZEBU15'], '64WI551TBNLAZEBU1502'], ['regression ["TD7FDXWKLVRV07ALBK"]', ['TD7FDXWKLVRV07ALBK'], 'TD7FDXWKLVRV07ALBK05'], ['control ["H6UNZ3Z93AZ7BYYPJC"]', ['H6UNZ3Z93AZ7BYYPJC'], 'H6UNZ3Z93AZ7BYYPJC84'], ['control ["2G388X3WHEMWPIB3DO"]', ['2G388X3WHEMWPIB3DO'], '2G388X3WHEMWPIB3DO38'], ['control ["WYITG3CIA2EMN51FG8"]', ['WYITG3CIA2EMN51FG8'], 'WYITG3CIA2EMN51FG854'], ['control ["X22YG0E1MY8V7QUQUU"]', ['X22YG0E1MY8V7QUQUU'], 'X22YG0E1MY8V7QUQUU47'], ['control ["3KL2WVMON87A9JVRD8"]', ['3KL2WVMON87A9JVRD8'], '3KL2WVMON87A9JVRD876'], ['control ["U6G55SH046WQ164I4P"]', ['U6G55SH046WQ164I4P'], 'U6G55SH046WQ164I4P20']], [['regression ["TD7FDXWKLVRV07ALBK"]', ['TD7FDXWKLVRV07ALBK'], 'TD7FDXWKLVRV07ALBK05'], ['regression ["64WI551TBNLAZEBU15"]', ['64WI551TBNLAZEBU15'], '64WI551TBNLAZEBU1502'], ['control ["U6G55SH046WQ164I4P"]', ['U6G55SH046WQ164I4P'], 'U6G55SH046WQ164I4P20'], ['control ["2Y76WQMSKZ26SJ35YB"]', ['2Y76WQMSKZ26SJ35YB'], '2Y76WQMSKZ26SJ35YB12'], ['control ["CU3JXPUYQHVR22PKEM"]', ['CU3JXPUYQHVR22PKEM'], 'CU3JXPUYQHVR22PKEM49'], ['control ["EPXGBGA2NLNHRPYT3N"]', ['EPXGBGA2NLNHRPYT3N'], 'EPXGBGA2NLNHRPYT3N83'], ['control ["BQGZ110JXMYQ68HH60"]', ['BQGZ110JXMYQ68HH60'], 'BQGZ110JXMYQ68HH6058'], ['control ["V6E7H467R3XXTF0UX2"]', ['V6E7H467R3XXTF0UX2'], 'V6E7H467R3XXTF0UX240']], [['regression ["64WI551TBNLAZEBU15"]', ['64WI551TBNLAZEBU15'], '64WI551TBNLAZEBU1502'], ['regression ["TD7FDXWKLVRV07ALBK"]', ['TD7FDXWKLVRV07ALBK'], 'TD7FDXWKLVRV07ALBK05'], ['control ["V6E7H467R3XXTF0UX2"]', ['V6E7H467R3XXTF0UX2'], 'V6E7H467R3XXTF0UX240'], ['control ["11H96GYM52SNV78B6G"]', ['11H96GYM52SNV78B6G'], '11H96GYM52SNV78B6G12'], ['control ["8WZS9XRTCO6DTNCKMU"]', ['8WZS9XRTCO6DTNCKMU'], '8WZS9XRTCO6DTNCKMU93'], ['control ["QBZJYTHC8GNQSKDJSD"]', ['QBZJYTHC8GNQSKDJSD'], 'QBZJYTHC8GNQSKDJSD15'], ['control ["PDZ2BB459ICKWDCEN4"]', ['PDZ2BB459ICKWDCEN4'], 'PDZ2BB459ICKWDCEN446'], ['control ["EMP8BUVSBRJMR8P6P0"]', ['EMP8BUVSBRJMR8P6P0'], 'EMP8BUVSBRJMR8P6P049']], [['regression ["TD7FDXWKLVRV07ALBK"]', ['TD7FDXWKLVRV07ALBK'], 'TD7FDXWKLVRV07ALBK05'], ['regression ["64WI551TBNLAZEBU15"]', ['64WI551TBNLAZEBU15'], '64WI551TBNLAZEBU1502'], ['control ["EMP8BUVSBRJMR8P6P0"]', ['EMP8BUVSBRJMR8P6P0'], 'EMP8BUVSBRJMR8P6P049'], ['control ["JA1SCUCU57DVVWD2MF"]', ['JA1SCUCU57DVVWD2MF'], 'JA1SCUCU57DVVWD2MF33'], ['control ["FUNIAT1L7171F0KBF9"]', ['FUNIAT1L7171F0KBF9'], 'FUNIAT1L7171F0KBF963'], ['control ["Z62YQ0YUTHLSESKG4A"]', ['Z62YQ0YUTHLSESKG4A'], 'Z62YQ0YUTHLSESKG4A79'], ['control ["5493001KJTIIGC8Y1R"]', ['5493001KJTIIGC8Y1R'], '5493001KJTIIGC8Y1R12'], ['control ["5493001kjtiigc8y1r"]', ['5493001kjtiigc8y1r'], '5493001KJTIIGC8Y1R12']]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression ["TD7FDXWKLVRV07ALBK"]	`TD7FDXWKLVRV07ALBK5`	`TD7FDXWKLVRV07ALBK05`	Failed
regression ["64WI551TBNLAZEBU15"]	`64WI551TBNLAZEBU152`	`64WI551TBNLAZEBU1502`	Failed
control ["NH4O4Q9HMI8RUJ0D6Y"]	`NH4O4Q9HMI8RUJ0D6Y73`	`NH4O4Q9HMI8RUJ0D6Y73`	Passed
control ["9K6IWOG7TS4VC3SHAM"]	`9K6IWOG7TS4VC3SHAM78`	`9K6IWOG7TS4VC3SHAM78`	Passed
control ["HTJBP9O1O9QSYUUD3R"]	`HTJBP9O1O9QSYUUD3R38`	`HTJBP9O1O9QSYUUD3R38`	Passed
control ["ACLPCCV3EGBW4QG3I6"]	`ACLPCCV3EGBW4QG3I685`	`ACLPCCV3EGBW4QG3I685`	Passed
control ["II5XCIYZ03SDPPSQ7Z"]	`II5XCIYZ03SDPPSQ7Z30`	`II5XCIYZ03SDPPSQ7Z30`	Passed
control ["H6UNZ3Z93AZ7BYYPJC"]	`H6UNZ3Z93AZ7BYYPJC84`	`H6UNZ3Z93AZ7BYYPJC84`	Passed

SHA-256 / 84b0f29de1e53678466c09fb84d9dc7e6706a3d40d8305895dc9e20cea224125

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(prefix):
    t = prefix.upper()
    if len(t) != 18 or not t.isascii() or not t.isalnum():
        return None
    n = int(''.join(str(int(ch, 36)) for ch in t + '00'))
    return t + '%2d' % (98 - n % 97)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['regression ["TD7FDXWKLVRV07ALBK"]', ['TD7FDXWKLVRV07ALBK'], 'TD7FDXWKLVRV07ALBK05'], ['regression ["64WI551TBNLAZEBU15"]', ['64WI551TBNLAZEBU15'], '64WI551TBNLAZEBU1502'], ['control ["NH4O4Q9HMI8RUJ0D6Y"]', ['NH4O4Q9HMI8RUJ0D6Y'], 'NH4O4Q9HMI8RUJ0D6Y73'], ['control ["9K6IWOG7TS4VC3SHAM"]', ['9K6IWOG7TS4VC3SHAM'], '9K6IWOG7TS4VC3SHAM78'], ['control ["HTJBP9O1O9QSYUUD3R"]', ['HTJBP9O1O9QSYUUD3R'], 'HTJBP9O1O9QSYUUD3R38'], ['control ["ACLPCCV3EGBW4QG3I6"]', ['ACLPCCV3EGBW4QG3I6'], 'ACLPCCV3EGBW4QG3I685'], ['control ["II5XCIYZ03SDPPSQ7Z"]', ['II5XCIYZ03SDPPSQ7Z'], 'II5XCIYZ03SDPPSQ7Z30'], ['control ["H6UNZ3Z93AZ7BYYPJC"]', ['H6UNZ3Z93AZ7BYYPJC'], 'H6UNZ3Z93AZ7BYYPJC84']], [['regression ["64WI551TBNLAZEBU15"]', ['64WI551TBNLAZEBU15'], '64WI551TBNLAZEBU1502'], ['regression ["TD7FDXWKLVRV07ALBK"]', ['TD7FDXWKLVRV07ALBK'], 'TD7FDXWKLVRV07ALBK05'], ['control ["H6UNZ3Z93AZ7BYYPJC"]', ['H6UNZ3Z93AZ7BYYPJC'], 'H6UNZ3Z93AZ7BYYPJC84'], ['control ["2G388X3WHEMWPIB3DO"]', ['2G388X3WHEMWPIB3DO'], '2G388X3WHEMWPIB3DO38'], ['control ["WYITG3CIA2EMN51FG8"]', ['WYITG3CIA2EMN51FG8'], 'WYITG3CIA2EMN51FG854'], ['control ["X22YG0E1MY8V7QUQUU"]', ['X22YG0E1MY8V7QUQUU'], 'X22YG0E1MY8V7QUQUU47'], ['control ["3KL2WVMON87A9JVRD8"]', ['3KL2WVMON87A9JVRD8'], '3KL2WVMON87A9JVRD876'], ['control ["U6G55SH046WQ164I4P"]', ['U6G55SH046WQ164I4P'], 'U6G55SH046WQ164I4P20']], [['regression ["TD7FDXWKLVRV07ALBK"]', ['TD7FDXWKLVRV07ALBK'], 'TD7FDXWKLVRV07ALBK05'], ['regression ["64WI551TBNLAZEBU15"]', ['64WI551TBNLAZEBU15'], '64WI551TBNLAZEBU1502'], ['control ["U6G55SH046WQ164I4P"]', ['U6G55SH046WQ164I4P'], 'U6G55SH046WQ164I4P20'], ['control ["2Y76WQMSKZ26SJ35YB"]', ['2Y76WQMSKZ26SJ35YB'], '2Y76WQMSKZ26SJ35YB12'], ['control ["CU3JXPUYQHVR22PKEM"]', ['CU3JXPUYQHVR22PKEM'], 'CU3JXPUYQHVR22PKEM49'], ['control ["EPXGBGA2NLNHRPYT3N"]', ['EPXGBGA2NLNHRPYT3N'], 'EPXGBGA2NLNHRPYT3N83'], ['control ["BQGZ110JXMYQ68HH60"]', ['BQGZ110JXMYQ68HH60'], 'BQGZ110JXMYQ68HH6058'], ['control ["V6E7H467R3XXTF0UX2"]', ['V6E7H467R3XXTF0UX2'], 'V6E7H467R3XXTF0UX240']], [['regression ["64WI551TBNLAZEBU15"]', ['64WI551TBNLAZEBU15'], '64WI551TBNLAZEBU1502'], ['regression ["TD7FDXWKLVRV07ALBK"]', ['TD7FDXWKLVRV07ALBK'], 'TD7FDXWKLVRV07ALBK05'], ['control ["V6E7H467R3XXTF0UX2"]', ['V6E7H467R3XXTF0UX2'], 'V6E7H467R3XXTF0UX240'], ['control ["11H96GYM52SNV78B6G"]', ['11H96GYM52SNV78B6G'], '11H96GYM52SNV78B6G12'], ['control ["8WZS9XRTCO6DTNCKMU"]', ['8WZS9XRTCO6DTNCKMU'], '8WZS9XRTCO6DTNCKMU93'], ['control ["QBZJYTHC8GNQSKDJSD"]', ['QBZJYTHC8GNQSKDJSD'], 'QBZJYTHC8GNQSKDJSD15'], ['control ["PDZ2BB459ICKWDCEN4"]', ['PDZ2BB459ICKWDCEN4'], 'PDZ2BB459ICKWDCEN446'], ['control ["EMP8BUVSBRJMR8P6P0"]', ['EMP8BUVSBRJMR8P6P0'], 'EMP8BUVSBRJMR8P6P049']], [['regression ["TD7FDXWKLVRV07ALBK"]', ['TD7FDXWKLVRV07ALBK'], 'TD7FDXWKLVRV07ALBK05'], ['regression ["64WI551TBNLAZEBU15"]', ['64WI551TBNLAZEBU15'], '64WI551TBNLAZEBU1502'], ['control ["EMP8BUVSBRJMR8P6P0"]', ['EMP8BUVSBRJMR8P6P0'], 'EMP8BUVSBRJMR8P6P049'], ['control ["JA1SCUCU57DVVWD2MF"]', ['JA1SCUCU57DVVWD2MF'], 'JA1SCUCU57DVVWD2MF33'], ['control ["FUNIAT1L7171F0KBF9"]', ['FUNIAT1L7171F0KBF9'], 'FUNIAT1L7171F0KBF963'], ['control ["Z62YQ0YUTHLSESKG4A"]', ['Z62YQ0YUTHLSESKG4A'], 'Z62YQ0YUTHLSESKG4A79'], ['control ["5493001KJTIIGC8Y1R"]', ['5493001KJTIIGC8Y1R'], '5493001KJTIIGC8Y1R12'], ['control ["5493001kjtiigc8y1r"]', ['5493001kjtiigc8y1r'], '5493001KJTIIGC8Y1R12']]]
for label, args, expected in fixtures[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)

Boundary fixture	Actual	Expected	Outcome
regression ["TD7FDXWKLVRV07ALBK"]	`TD7FDXWKLVRV07ALBK 5`	`TD7FDXWKLVRV07ALBK05`	Failed
regression ["64WI551TBNLAZEBU15"]	`64WI551TBNLAZEBU15 2`	`64WI551TBNLAZEBU1502`	Failed
control ["NH4O4Q9HMI8RUJ0D6Y"]	`NH4O4Q9HMI8RUJ0D6Y73`	`NH4O4Q9HMI8RUJ0D6Y73`	Passed
control ["9K6IWOG7TS4VC3SHAM"]	`9K6IWOG7TS4VC3SHAM78`	`9K6IWOG7TS4VC3SHAM78`	Passed
control ["HTJBP9O1O9QSYUUD3R"]	`HTJBP9O1O9QSYUUD3R38`	`HTJBP9O1O9QSYUUD3R38`	Passed
control ["ACLPCCV3EGBW4QG3I6"]	`ACLPCCV3EGBW4QG3I685`	`ACLPCCV3EGBW4QG3I685`	Passed
control ["II5XCIYZ03SDPPSQ7Z"]	`II5XCIYZ03SDPPSQ7Z30`	`II5XCIYZ03SDPPSQ7Z30`	Passed
control ["H6UNZ3Z93AZ7BYYPJC"]	`H6UNZ3Z93AZ7BYYPJC84`	`H6UNZ3Z93AZ7BYYPJC84`	Passed

SHA-256 / 42477a76acbf4703a1984371e242e276e4fe22cf8936f200aef06d64f6fc07ac

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

Verification & scope

A deterministic, bounded teaching model of the named scheme under the stated contract; not a certified validator. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:48:41.502641+00:00.

Case digest / 36b73aa311a268ec92c5048bb77fd5938a339c002bc8c094743da9ab593fda07