FA-2951 / Encodings / Open access

Latin-1 bytes are decoded through a typographic code page · case 01

Latin-1 bytes are decoded through a typographic code page.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The implementation applies an operation whose text or grammar semantics violate this contract: Decode every byte one-to-one as ISO-8859-1.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Decode every byte one-to-one as ISO-8859-1.

Unsuccessful approach: The attempted repair handles the primary example but still violates a separate boundary of the same contract.

Case contract

Decode every byte one-to-one as ISO-8859-1.

Why this case matters

A local executable model for consumers of structured text; oracle values are authored literals, not outputs copied from the repaired implementation.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return bytes.fromhex(x).decode('utf-8','replace')
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('80'), '\x80')
check('boundary 2', solve('ff'), 'ÿ')
check('boundary 3', solve('41'), 'A')
check('boundary 4', solve(''), '')
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
boundary 1	`�`		Failed
boundary 2	`�`	`ÿ`	Failed
boundary 3	`A`	`A`	Passed
boundary 4			Passed

SHA-256 / 53d7f37759fcf9aeabacb2689bba510b54c47bbe804f3ac1d03ef87467e2c052

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return bytes.fromhex(x).decode('cp1252','replace')
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('80'), '\x80')
check('boundary 2', solve('ff'), 'ÿ')
check('boundary 3', solve('41'), 'A')
check('boundary 4', solve(''), '')
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
boundary 1	`€`		Failed
boundary 2	`ÿ`	`ÿ`	Passed
boundary 3	`A`	`A`	Passed
boundary 4			Passed

SHA-256 / 5f2b4a0b2569b22cae28fb4bbca4c3f7fc7dd3521ef40326c2f7a557576f2dc5

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
import re, unicodedata, json, csv, io, html, base64, binascii, codecs, struct
from urllib.parse import quote, unquote, unquote_to_bytes, urlencode, parse_qsl, urlsplit, urlunsplit
from email.header import decode_header, make_header
from email.utils import getaddresses
from xml.etree import ElementTree as ET
import shlex, string, textwrap

N = 1
observations = []
def solve(x):
    try:
        return bytes.fromhex(x).decode('latin-1')
    except Exception as exc:
        return {"error": type(exc).__name__}
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('boundary 1', solve('80'), '\x80')
check('boundary 2', solve('ff'), 'ÿ')
check('boundary 3', solve('41'), 'A')
check('boundary 4', solve(''), '')
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
boundary 1			Passed
boundary 2	`ÿ`	`ÿ`	Passed
boundary 3	`A`	`A`	Passed
boundary 4			Passed

SHA-256 / 1078122582e0f7ecdd7e84eaf54174a1401f86ab87f8000d42dd96140a3687b5

Verification & scope

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 2026-09-29T14:37:19.514578+00:00.

Case digest / c209967f3d026d0facbf3f1f78e4eff7b7f4f2342fa6496b0ebeee1bea5a0475