FA-95916 / Postal address normalization / Open access

Five-or-nine digit postal code: letters pass as code digits · case 01

"1203O" with a letter O is returned as a valid code.

Verified by executionVariant 1 · 12 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The character-class test is missing, so only the length is checked.

VERIFIED REPAIR

Require every character to be a digit.

Unsuccessful approach: Requiring alphanumeric characters still admits the letter O.

Case contract

Input a string or an integer. Integers are zero-padded to 5 digits when <= 99999, else to 9. Strings are stripped; a 10-character string with "-" or a space at index 5 loses that separator. Valid results are exactly 5 or 9 ASCII digits; 9 digits render "DDDDD-DDDD" unless the last four are "0000", which renders the 5-digit form. Anything else returns None.

Why this case matters

Postal codes arrive from spreadsheets, forms and legacy files; losing leading zeros or accepting malformed codes misroutes mail and breaks deduplication.

1 / The failure

Exit 1

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

N = 1
observations = []
def solve(x):
    if isinstance(x, int):
        s = str(x).zfill(5) if x <= 99999 else str(x).zfill(9)
    else:
        s = x.strip()
        if len(s) == 10 and s[5] in '- ':
            s = s[:5] + s[6:]
    if len(s) not in (5, 9):
        return None
    if len(s) == 9 and s[5:] != '0000':
        return s[:5] + '-' + s[5:]
    return s[:5]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['plain five-digit code', '12039', '12039'], ['hyphenated plus-four', '12039-4101', '12039-4101'], ['space-separated plus-four', '12039 4101', '12039-4101'], ['spreadsheet integer lost its leading zero', 1231, '01231'], ['eight-digit integer is a nine-digit code with a leading zero', 12345671, '01234-5671'], ['zero plus-four is dropped', '12039-0000', '12039'], ['plus-four ending in three zeros is kept', '12039-2000', '12039-2000'], ['seven digits rejected', '1203912', None], ['ten digits without separator rejected', '1203941017', None], ['slash separator rejected', '12039/4101', None], ['letter O is not zero', '1203O', None], ['surrounding whitespace trimmed', ' 12039\n', '12039']], [['plain five-digit code', '23049', '23049'], ['hyphenated plus-four', '23049-5102', '23049-5102'], ['space-separated plus-four', '23049 5102', '23049-5102'], ['spreadsheet integer lost its leading zero', 1232, '01232'], ['eight-digit integer is a nine-digit code with a leading zero', 12345672, '01234-5672'], ['zero plus-four is dropped', '23049-0000', '23049'], ['plus-four ending in three zeros is kept', '23049-3000', '23049-3000'], ['seven digits rejected', '2304912', None], ['ten digits without separator rejected', '2304951027', None], ['slash separator rejected', '23049/5102', None], ['letter O is not zero', '2304O', None], ['surrounding whitespace trimmed', ' 23049\n', '23049']], [['plain five-digit code', '34059', '34059'], ['hyphenated plus-four', '34059-6103', '34059-6103'], ['space-separated plus-four', '34059 6103', '34059-6103'], ['spreadsheet integer lost its leading zero', 1233, '01233'], ['eight-digit integer is a nine-digit code with a leading zero', 12345673, '01234-5673'], ['zero plus-four is dropped', '34059-0000', '34059'], ['plus-four ending in three zeros is kept', '34059-4000', '34059-4000'], ['seven digits rejected', '3405912', None], ['ten digits without separator rejected', '3405961037', None], ['slash separator rejected', '34059/6103', None], ['letter O is not zero', '3405O', None], ['surrounding whitespace trimmed', ' 34059\n', '34059']], [['plain five-digit code', '45069', '45069'], ['hyphenated plus-four', '45069-7104', '45069-7104'], ['space-separated plus-four', '45069 7104', '45069-7104'], ['spreadsheet integer lost its leading zero', 1234, '01234'], ['eight-digit integer is a nine-digit code with a leading zero', 12345674, '01234-5674'], ['zero plus-four is dropped', '45069-0000', '45069'], ['plus-four ending in three zeros is kept', '45069-5000', '45069-5000'], ['seven digits rejected', '4506912', None], ['ten digits without separator rejected', '4506971047', None], ['slash separator rejected', '45069/7104', None], ['letter O is not zero', '4506O', None], ['surrounding whitespace trimmed', ' 45069\n', '45069']], [['plain five-digit code', '56079', '56079'], ['hyphenated plus-four', '56079-8105', '56079-8105'], ['space-separated plus-four', '56079 8105', '56079-8105'], ['spreadsheet integer lost its leading zero', 1235, '01235'], ['eight-digit integer is a nine-digit code with a leading zero', 12345675, '01234-5675'], ['zero plus-four is dropped', '56079-0000', '56079'], ['plus-four ending in three zeros is kept', '56079-6000', '56079-6000'], ['seven digits rejected', '5607912', None], ['ten digits without separator rejected', '5607981057', None], ['slash separator rejected', '56079/8105', None], ['letter O is not zero', '5607O', None], ['surrounding whitespace trimmed', ' 56079\n', '56079']]]
for label, arg, expected in fixtures[N - 1]:
    check(label, solve(arg), 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
plain five-digit code	`12039`	`12039`	Passed
hyphenated plus-four	`12039-4101`	`12039-4101`	Passed
space-separated plus-four	`12039-4101`	`12039-4101`	Passed
spreadsheet integer lost its leading zero	`01231`	`01231`	Passed
eight-digit integer is a nine-digit code with a leading zero	`01234-5671`	`01234-5671`	Passed
zero plus-four is dropped	`12039`	`12039`	Passed
plus-four ending in three zeros is kept	`12039-2000`	`12039-2000`	Passed
seven digits rejected	`None`	`None`	Passed
ten digits without separator rejected	`None`	`None`	Passed
slash separator rejected	`None`	`None`	Passed
letter O is not zero	`1203O`	`None`	Failed
surrounding whitespace trimmed	`12039`	`12039`	Passed

SHA-256 / b51e862e50a9d395df998256c6ee6350ac4bf4a05e0932ef7bd7d7152e1dd5fa

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(x):
    if isinstance(x, int):
        s = str(x).zfill(5) if x <= 99999 else str(x).zfill(9)
    else:
        s = x.strip()
        if len(s) == 10 and s[5] in '- ':
            s = s[:5] + s[6:]
    if len(s) not in (5, 9) or not s.isalnum():
        return None
    if len(s) == 9 and s[5:] != '0000':
        return s[:5] + '-' + s[5:]
    return s[:5]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['plain five-digit code', '12039', '12039'], ['hyphenated plus-four', '12039-4101', '12039-4101'], ['space-separated plus-four', '12039 4101', '12039-4101'], ['spreadsheet integer lost its leading zero', 1231, '01231'], ['eight-digit integer is a nine-digit code with a leading zero', 12345671, '01234-5671'], ['zero plus-four is dropped', '12039-0000', '12039'], ['plus-four ending in three zeros is kept', '12039-2000', '12039-2000'], ['seven digits rejected', '1203912', None], ['ten digits without separator rejected', '1203941017', None], ['slash separator rejected', '12039/4101', None], ['letter O is not zero', '1203O', None], ['surrounding whitespace trimmed', ' 12039\n', '12039']], [['plain five-digit code', '23049', '23049'], ['hyphenated plus-four', '23049-5102', '23049-5102'], ['space-separated plus-four', '23049 5102', '23049-5102'], ['spreadsheet integer lost its leading zero', 1232, '01232'], ['eight-digit integer is a nine-digit code with a leading zero', 12345672, '01234-5672'], ['zero plus-four is dropped', '23049-0000', '23049'], ['plus-four ending in three zeros is kept', '23049-3000', '23049-3000'], ['seven digits rejected', '2304912', None], ['ten digits without separator rejected', '2304951027', None], ['slash separator rejected', '23049/5102', None], ['letter O is not zero', '2304O', None], ['surrounding whitespace trimmed', ' 23049\n', '23049']], [['plain five-digit code', '34059', '34059'], ['hyphenated plus-four', '34059-6103', '34059-6103'], ['space-separated plus-four', '34059 6103', '34059-6103'], ['spreadsheet integer lost its leading zero', 1233, '01233'], ['eight-digit integer is a nine-digit code with a leading zero', 12345673, '01234-5673'], ['zero plus-four is dropped', '34059-0000', '34059'], ['plus-four ending in three zeros is kept', '34059-4000', '34059-4000'], ['seven digits rejected', '3405912', None], ['ten digits without separator rejected', '3405961037', None], ['slash separator rejected', '34059/6103', None], ['letter O is not zero', '3405O', None], ['surrounding whitespace trimmed', ' 34059\n', '34059']], [['plain five-digit code', '45069', '45069'], ['hyphenated plus-four', '45069-7104', '45069-7104'], ['space-separated plus-four', '45069 7104', '45069-7104'], ['spreadsheet integer lost its leading zero', 1234, '01234'], ['eight-digit integer is a nine-digit code with a leading zero', 12345674, '01234-5674'], ['zero plus-four is dropped', '45069-0000', '45069'], ['plus-four ending in three zeros is kept', '45069-5000', '45069-5000'], ['seven digits rejected', '4506912', None], ['ten digits without separator rejected', '4506971047', None], ['slash separator rejected', '45069/7104', None], ['letter O is not zero', '4506O', None], ['surrounding whitespace trimmed', ' 45069\n', '45069']], [['plain five-digit code', '56079', '56079'], ['hyphenated plus-four', '56079-8105', '56079-8105'], ['space-separated plus-four', '56079 8105', '56079-8105'], ['spreadsheet integer lost its leading zero', 1235, '01235'], ['eight-digit integer is a nine-digit code with a leading zero', 12345675, '01234-5675'], ['zero plus-four is dropped', '56079-0000', '56079'], ['plus-four ending in three zeros is kept', '56079-6000', '56079-6000'], ['seven digits rejected', '5607912', None], ['ten digits without separator rejected', '5607981057', None], ['slash separator rejected', '56079/8105', None], ['letter O is not zero', '5607O', None], ['surrounding whitespace trimmed', ' 56079\n', '56079']]]
for label, arg, expected in fixtures[N - 1]:
    check(label, solve(arg), 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
plain five-digit code	`12039`	`12039`	Passed
hyphenated plus-four	`12039-4101`	`12039-4101`	Passed
space-separated plus-four	`12039-4101`	`12039-4101`	Passed
spreadsheet integer lost its leading zero	`01231`	`01231`	Passed
eight-digit integer is a nine-digit code with a leading zero	`01234-5671`	`01234-5671`	Passed
zero plus-four is dropped	`12039`	`12039`	Passed
plus-four ending in three zeros is kept	`12039-2000`	`12039-2000`	Passed
seven digits rejected	`None`	`None`	Passed
ten digits without separator rejected	`None`	`None`	Passed
slash separator rejected	`None`	`None`	Passed
letter O is not zero	`1203O`	`None`	Failed
surrounding whitespace trimmed	`12039`	`12039`	Passed

SHA-256 / 9e81fcc2f4bdbe5f5d62646124e680fde6b12facf7795e103e2ec967ce95a3b4

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(x):
    if isinstance(x, int):
        s = str(x).zfill(5) if x <= 99999 else str(x).zfill(9)
    else:
        s = x.strip()
        if len(s) == 10 and s[5] in '- ':
            s = s[:5] + s[6:]
    if len(s) not in (5, 9) or not s.isdigit():
        return None
    if len(s) == 9 and s[5:] != '0000':
        return s[:5] + '-' + s[5:]
    return s[:5]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[['plain five-digit code', '12039', '12039'], ['hyphenated plus-four', '12039-4101', '12039-4101'], ['space-separated plus-four', '12039 4101', '12039-4101'], ['spreadsheet integer lost its leading zero', 1231, '01231'], ['eight-digit integer is a nine-digit code with a leading zero', 12345671, '01234-5671'], ['zero plus-four is dropped', '12039-0000', '12039'], ['plus-four ending in three zeros is kept', '12039-2000', '12039-2000'], ['seven digits rejected', '1203912', None], ['ten digits without separator rejected', '1203941017', None], ['slash separator rejected', '12039/4101', None], ['letter O is not zero', '1203O', None], ['surrounding whitespace trimmed', ' 12039\n', '12039']], [['plain five-digit code', '23049', '23049'], ['hyphenated plus-four', '23049-5102', '23049-5102'], ['space-separated plus-four', '23049 5102', '23049-5102'], ['spreadsheet integer lost its leading zero', 1232, '01232'], ['eight-digit integer is a nine-digit code with a leading zero', 12345672, '01234-5672'], ['zero plus-four is dropped', '23049-0000', '23049'], ['plus-four ending in three zeros is kept', '23049-3000', '23049-3000'], ['seven digits rejected', '2304912', None], ['ten digits without separator rejected', '2304951027', None], ['slash separator rejected', '23049/5102', None], ['letter O is not zero', '2304O', None], ['surrounding whitespace trimmed', ' 23049\n', '23049']], [['plain five-digit code', '34059', '34059'], ['hyphenated plus-four', '34059-6103', '34059-6103'], ['space-separated plus-four', '34059 6103', '34059-6103'], ['spreadsheet integer lost its leading zero', 1233, '01233'], ['eight-digit integer is a nine-digit code with a leading zero', 12345673, '01234-5673'], ['zero plus-four is dropped', '34059-0000', '34059'], ['plus-four ending in three zeros is kept', '34059-4000', '34059-4000'], ['seven digits rejected', '3405912', None], ['ten digits without separator rejected', '3405961037', None], ['slash separator rejected', '34059/6103', None], ['letter O is not zero', '3405O', None], ['surrounding whitespace trimmed', ' 34059\n', '34059']], [['plain five-digit code', '45069', '45069'], ['hyphenated plus-four', '45069-7104', '45069-7104'], ['space-separated plus-four', '45069 7104', '45069-7104'], ['spreadsheet integer lost its leading zero', 1234, '01234'], ['eight-digit integer is a nine-digit code with a leading zero', 12345674, '01234-5674'], ['zero plus-four is dropped', '45069-0000', '45069'], ['plus-four ending in three zeros is kept', '45069-5000', '45069-5000'], ['seven digits rejected', '4506912', None], ['ten digits without separator rejected', '4506971047', None], ['slash separator rejected', '45069/7104', None], ['letter O is not zero', '4506O', None], ['surrounding whitespace trimmed', ' 45069\n', '45069']], [['plain five-digit code', '56079', '56079'], ['hyphenated plus-four', '56079-8105', '56079-8105'], ['space-separated plus-four', '56079 8105', '56079-8105'], ['spreadsheet integer lost its leading zero', 1235, '01235'], ['eight-digit integer is a nine-digit code with a leading zero', 12345675, '01234-5675'], ['zero plus-four is dropped', '56079-0000', '56079'], ['plus-four ending in three zeros is kept', '56079-6000', '56079-6000'], ['seven digits rejected', '5607912', None], ['ten digits without separator rejected', '5607981057', None], ['slash separator rejected', '56079/8105', None], ['letter O is not zero', '5607O', None], ['surrounding whitespace trimmed', ' 56079\n', '56079']]]
for label, arg, expected in fixtures[N - 1]:
    check(label, solve(arg), 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
plain five-digit code	`12039`	`12039`	Passed
hyphenated plus-four	`12039-4101`	`12039-4101`	Passed
space-separated plus-four	`12039-4101`	`12039-4101`	Passed
spreadsheet integer lost its leading zero	`01231`	`01231`	Passed
eight-digit integer is a nine-digit code with a leading zero	`01234-5671`	`01234-5671`	Passed
zero plus-four is dropped	`12039`	`12039`	Passed
plus-four ending in three zeros is kept	`12039-2000`	`12039-2000`	Passed
seven digits rejected	`None`	`None`	Passed
ten digits without separator rejected	`None`	`None`	Passed
slash separator rejected	`None`	`None`	Passed
letter O is not zero	`None`	`None`	Passed
surrounding whitespace trimmed	`12039`	`12039`	Passed

SHA-256 / c32795b8a0f49bfd0ad869ca6928cdd31471271c1cfa784b88444a76fd3d1495

Verification & scope

A deterministic toy contract over synthetic, obviously fictitious addresses. The rules are stipulated for this model only and make no claim of conformance with any postal authority standard. 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 2026-09-29T14:52:18.079537+00:00.

Case digest / 141b0d5e3a08521f103f50a2fe055263b5aa46986156a63c1d2dfffc4312bdda