{"abstract":"The operation returns a result or retained state that violates this contract: Zip to exhaustion of both inputs and fill missing positions with a distinct string marker; present None is retained.","category":"Iterator consumption","checks":4,"contract":"Zip to exhaustion of both inputs and fill missing positions with a distinct string marker; present None is retained. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","evaluation_group":"model-87a2359373893feb","failed_approach":"Replacing all None values with padding changes legitimate present None values.","family":"xr-zip-longest-distinguishes-real-none","id":"FA-4611","implementations":{"attempt":{"sha256":"9349a990a5ebebd0e09ad3c738d9d11ec2cbe40f3f4ba15a5527832aecc384c3","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport itertools as it\nfrom collections import deque\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return [[\"missing\" if v is None else v for v in row] for row in it.zip_longest(x,y)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('present None retained', solve([None], ['a', 'b']), [[None, 'a'], ['missing', 'b']])\ncheck('empty left', solve([], ['a']), [['missing', 'a']])\ncheck('empty both', solve([], []), [])\ncheck('empty right', solve(['a'], []), [['a', 'missing']])\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"broken":{"sha256":"8020c7dc95a326c183cc14f113f7be8a2fb23849df01c9e3266457168bb1b562","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport itertools as it\nfrom collections import deque\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return [list(v) for v in zip(x,y)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('present None retained', solve([None], ['a', 'b']), [[None, 'a'], ['missing', 'b']])\ncheck('empty left', solve([], ['a']), [['missing', 'a']])\ncheck('empty both', solve([], []), [])\ncheck('empty right', solve(['a'], []), [['a', 'missing']])\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"},"fixed":{"sha256":"43833478ff62aaf9c948c4e7488bddd56f3c4a0665bde704c5638acabe8dff2f","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\nimport itertools as it\nfrom collections import deque\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return [list(v) for v in it.zip_longest(x,y,fillvalue=\"missing\")]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('present None retained', solve([None], ['a', 'b']), [[None, 'a'], ['missing', 'b']])\ncheck('empty left', solve([], ['a']), [['missing', 'a']])\ncheck('empty both', solve([], []), [])\ncheck('empty right', solve(['a'], []), [['a', 'missing']])\nprint(json.dumps({\"observations\": observations, \"passed\": all(x[\"passed\"] for x in observations)}, ensure_ascii=False))\nraise SystemExit(0 if all(x[\"passed\"] for x in observations) else 1)\n"}},"limitations":" 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.","method":"Deterministic executable model with adversarial boundary fixtures.","provenance":{"created_by":"Failure Map","dependencies":"Python standard library","family":"xr-zip-longest-distinguishes-real-none","generated_at":"2026-09-29T14:37:40.915869+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.","repair":"Zip to exhaustion of both inputs and fill missing positions with a distinct string marker; present None is retained.","root_cause":"Ordinary zip discards the longer suffix.","sha256":"aa74f86992813422a46fcb632c091f64ae5f49e13f0bd73e1c5b62ff7abf1c35","title":"Zip longest distinguishes real none · case 01","variant":1,"variant_policy":"Five execution reruns of a fixed adversarial fixture suite; variant number does not alter semantic inputs.","verification":{"attempt":{"elapsed_ms":36.848,"exit_code":1,"observations":[{"actual":[["missing","a"],["missing","b"]],"check":"present None retained","expected":[[null,"a"],["missing","b"]],"passed":false},{"actual":[["missing","a"]],"check":"empty left","expected":[["missing","a"]],"passed":true},{"actual":[],"check":"empty both","expected":[],"passed":true},{"actual":[["a","missing"]],"check":"empty right","expected":[["a","missing"]],"passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"present None retained\", \"actual\": [[\"missing\", \"a\"], [\"missing\", \"b\"]], \"expected\": [[null, \"a\"], [\"missing\", \"b\"]], \"passed\": false}, {\"check\": \"empty left\", \"actual\": [[\"missing\", \"a\"]], \"expected\": [[\"missing\", \"a\"]], \"passed\": true}, {\"check\": \"empty both\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right\", \"actual\": [[\"a\", \"missing\"]], \"expected\": [[\"a\", \"missing\"]], \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":34.664,"exit_code":1,"observations":[{"actual":[[null,"a"]],"check":"present None retained","expected":[[null,"a"],["missing","b"]],"passed":false},{"actual":[],"check":"empty left","expected":[["missing","a"]],"passed":false},{"actual":[],"check":"empty both","expected":[],"passed":true},{"actual":[],"check":"empty right","expected":[["a","missing"]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"present None retained\", \"actual\": [[null, \"a\"]], \"expected\": [[null, \"a\"], [\"missing\", \"b\"]], \"passed\": false}, {\"check\": \"empty left\", \"actual\": [], \"expected\": [[\"missing\", \"a\"]], \"passed\": false}, {\"check\": \"empty both\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right\", \"actual\": [], \"expected\": [[\"a\", \"missing\"]], \"passed\": false}], \"passed\": false}\n"},"fixed":{"elapsed_ms":38.002,"exit_code":0,"observations":[{"actual":[[null,"a"],["missing","b"]],"check":"present None retained","expected":[[null,"a"],["missing","b"]],"passed":true},{"actual":[["missing","a"]],"check":"empty left","expected":[["missing","a"]],"passed":true},{"actual":[],"check":"empty both","expected":[],"passed":true},{"actual":[["a","missing"]],"check":"empty right","expected":[["a","missing"]],"passed":true}],"passed":true,"stderr":"","stdout":"{\"observations\": [{\"check\": \"present None retained\", \"actual\": [[null, \"a\"], [\"missing\", \"b\"]], \"expected\": [[null, \"a\"], [\"missing\", \"b\"]], \"passed\": true}, {\"check\": \"empty left\", \"actual\": [[\"missing\", \"a\"]], \"expected\": [[\"missing\", \"a\"]], \"passed\": true}, {\"check\": \"empty both\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right\", \"actual\": [[\"a\", \"missing\"]], \"expected\": [[\"a\", \"missing\"]], \"passed\": true}], \"passed\": true}\n"}},"verified":true,"visibility":"public"}