{"abstract":"The operation returns a result or retained state that violates this contract: Zip to the longer operand, using None for absent positions.","category":"Collection algebra","checks":5,"contract":"Zip to the longer operand, using None for absent positions. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.","contract_signature":"x, y=None","evaluation_group":"model-12361b19210d9f16","failed_approach":"Cycling the shorter input fabricates values where padding is required.","family":"xr-zip-longest-explicit-padding","id":"FA-4276","implementations":{"attempt":{"sha256":"1bdccdfb624830994003fe63e21ae13cd3c98957dcfd6b601ddfc76938373b40","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return [[x[i%len(x)] if x else None,y[i%len(y)] if y else None] for i in range(max(len(x),len(y)))]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('both empty', solve([], []), [])\ncheck('empty right operand', solve(['a'], []), [['a', None]])\ncheck('empty left operand', solve([], ['b']), [[None, 'b']])\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), [['b', 'b'], ['a', 'c'], ['b', 'c']])\ncheck('padding must not cycle shorter side', solve(['a'], ['b','c']), [['a','b'],[None,'c']])\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":"a669de2d66a6cadc34cef1397e325e9e926c2d85d167436de93895eeec13c1db","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(x, y=None):\n    return [[a,b] for a,b in zip(x,y)]\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('both empty', solve([], []), [])\ncheck('empty right operand', solve(['a'], []), [['a', None]])\ncheck('empty left operand', solve([], ['b']), [[None, 'b']])\ncheck('overlap and multiplicity', solve(['b', 'a', 'b'], ['b', 'c', 'c']), [['b', 'b'], ['a', 'c'], ['b', 'c']])\ncheck('padding must not cycle shorter side', solve(['a'], ['b','c']), [['a','b'],[None,'c']])\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-explicit-padding","generated_at":"2026-09-29T14:37:37.534968+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.","root_cause":"Ordinary zip truncates the longer input.","sha256":"fb27b1b1e7657a9184333cc8105f581d75ae7bcfa84d9d72b6ba6965100b171a","title":"Zip longest explicit padding · case 01","variant":1,"variant_policy":"Five execution reruns of a fixed adversarial fixture suite; variant number does not alter semantic inputs.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":36.987,"exit_code":1,"observations":[{"actual":[],"check":"both empty","expected":[],"passed":true},{"actual":[["a",null]],"check":"empty right operand","expected":[["a",null]],"passed":true},{"actual":[[null,"b"]],"check":"empty left operand","expected":[[null,"b"]],"passed":true},{"actual":[["b","b"],["a","c"],["b","c"]],"check":"overlap and multiplicity","expected":[["b","b"],["a","c"],["b","c"]],"passed":true},{"actual":[["a","b"],["a","c"]],"check":"padding must not cycle shorter side","expected":[["a","b"],[null,"c"]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": [[\"a\", null]], \"expected\": [[\"a\", null]], \"passed\": true}, {\"check\": \"empty left operand\", \"actual\": [[null, \"b\"]], \"expected\": [[null, \"b\"]], \"passed\": true}, {\"check\": \"overlap and multiplicity\", \"actual\": [[\"b\", \"b\"], [\"a\", \"c\"], [\"b\", \"c\"]], \"expected\": [[\"b\", \"b\"], [\"a\", \"c\"], [\"b\", \"c\"]], \"passed\": true}, {\"check\": \"padding must not cycle shorter side\", \"actual\": [[\"a\", \"b\"], [\"a\", \"c\"]], \"expected\": [[\"a\", \"b\"], [null, \"c\"]], \"passed\": false}], \"passed\": false}\n"},"broken":{"elapsed_ms":40.466,"exit_code":1,"observations":[{"actual":[],"check":"both empty","expected":[],"passed":true},{"actual":[],"check":"empty right operand","expected":[["a",null]],"passed":false},{"actual":[],"check":"empty left operand","expected":[[null,"b"]],"passed":false},{"actual":[["b","b"],["a","c"],["b","c"]],"check":"overlap and multiplicity","expected":[["b","b"],["a","c"],["b","c"]],"passed":true},{"actual":[["a","b"]],"check":"padding must not cycle shorter side","expected":[["a","b"],[null,"c"]],"passed":false}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"both empty\", \"actual\": [], \"expected\": [], \"passed\": true}, {\"check\": \"empty right operand\", \"actual\": [], \"expected\": [[\"a\", null]], \"passed\": false}, {\"check\": \"empty left operand\", \"actual\": [], \"expected\": [[null, \"b\"]], \"passed\": false}, {\"check\": \"overlap and multiplicity\", \"actual\": [[\"b\", \"b\"], [\"a\", \"c\"], [\"b\", \"c\"]], \"expected\": [[\"b\", \"b\"], [\"a\", \"c\"], [\"b\", \"c\"]], \"passed\": true}, {\"check\": \"padding must not cycle shorter side\", \"actual\": [[\"a\", \"b\"]], \"expected\": [[\"a\", \"b\"], [null, \"c\"]], \"passed\": false}], \"passed\": false}\n"}},"member_only":{"stages":["fixed"],"fields":["implementations.fixed","verification.fixed","harness","repair"],"note":"The verified repair, its recorded checks, the repair description, and the scoring harness are available to members."}}