FA-4036 / Binary formats / Open access

Hex formatting places a separator between nybbles · case 01

Hex formatting places a separator between nybbles.

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: Format bytes as lowercase two-digit hex groups separated by one colon; empty input empty.

VERIFIED REPAIR

Implement the complete stated contract, including the boundary fixtures: Format bytes as lowercase two-digit hex groups separated by one colon; empty input empty.

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

Case contract

Format bytes as lowercase two-digit hex groups separated by one colon; empty input empty.

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 ':'.join(bytes(x).hex())
    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([0, 10, 255]), '00:0a:ff')
check('boundary 2', solve([16]), '10')
check('boundary 3', solve([]), '')
check('boundary 4', solve([1, 2]), '01:02')
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	`0:0:0:a:f:f`	`00:0a:ff`	Failed
boundary 2	`1:0`	`10`	Failed
boundary 3			Passed
boundary 4	`0:1:0:2`	`01:02`	Failed

SHA-256 / 09318218cf917aa9e18023d69ca5ece4675a81ee74e2a70de9394a9d543d6953

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 ':'.join(format(v,'x') for v in x)
    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([0, 10, 255]), '00:0a:ff')
check('boundary 2', solve([16]), '10')
check('boundary 3', solve([]), '')
check('boundary 4', solve([1, 2]), '01:02')
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	`0:a:ff`	`00:0a:ff`	Failed
boundary 2	`10`	`10`	Passed
boundary 3			Passed
boundary 4	`1:2`	`01:02`	Failed

SHA-256 / 25b8896dc8bb2ca5a2d21c73344ec0356a05d8b1f120dff771484e0deae82395

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(x).hex(':')
    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([0, 10, 255]), '00:0a:ff')
check('boundary 2', solve([16]), '10')
check('boundary 3', solve([]), '')
check('boundary 4', solve([1, 2]), '01:02')
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	`00:0a:ff`	`00:0a:ff`	Passed
boundary 2	`10`	`10`	Passed
boundary 3			Passed
boundary 4	`01:02`	`01:02`	Passed

SHA-256 / fd3aa531271c7ec9d13c8a41065ba0d69a446faf44f629514a315dadebbb9137

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 2026-09-29T14:37:34.633744+00:00.

Case digest / 2414753db08e073128e30e41852f4a96c3b349b9bb1289c599e44630604a8149