{"abstract":"Changes the omitted second-argument default and changes the required Python-language result.","category":"Call argument binding","checks":6,"contract":"Call f(a, /, b=10) and return [a,b]. The first parameter is required and positional-only; b accepts position or keyword. Inputs use the finite Python types shown in the fixtures. An error string denotes the specified caught exception, not an unhandled process failure.","contract_signature":"args, kwargs","evaluation_group":"xl-positional-only-binding","failed_approach":"The alternative still fails because it adds a default to the required first parameter.","family":"xl-positional-only-binding-default-drift","id":"FA-4846","implementations":{"attempt":{"sha256":"fa0f1cbd4589c0595774fb459e67615b54d8660c49eeac9b9aaeeec8a557e370","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(args, kwargs):\n    def f(a=0, /, b=10):\n        return [a,b]\n    try:\n        return f(*args, **kwargs)\n    except TypeError:\n        return \"TypeError\"\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('keyword first rejected', solve([], {'a': 1}), 'TypeError')\ncheck('omitted optional', solve([1], {}), [1, 10])\ncheck('two positions', solve([1, 2], {}), [1, 2])\ncheck('named second', solve([1], {'b': 3}), [1, 3])\ncheck('missing first', solve([], {}), 'TypeError')\ncheck('duplicate apparent first', solve([1], {'a': 2}), 'TypeError')\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":"e281190fad5fa06ccb1c95904bfbb058243d50b5ab40b9baf4800fba8dc6d58b","source":"\"\"\"Failure Map reference implementation. Python standard library only.\"\"\"\nimport json\n\nN = 1\nobservations = []\ndef solve(args, kwargs):\n    def f(a, /, b=None):\n        return [a,b]\n    try:\n        return f(*args, **kwargs)\n    except TypeError:\n        return \"TypeError\"\ndef check(label, actual, expected):\n    observations.append({\"check\": label, \"actual\": actual, \"expected\": expected, \"passed\": actual == expected})\ncheck('keyword first rejected', solve([], {'a': 1}), 'TypeError')\ncheck('omitted optional', solve([1], {}), [1, 10])\ncheck('two positions', solve([1, 2], {}), [1, 2])\ncheck('named second', solve([1], {'b': 3}), [1, 3])\ncheck('missing first', solve([], {}), 'TypeError')\ncheck('duplicate apparent first', solve([1], {'a': 2}), 'TypeError')\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":"xl-positional-only-binding-default-drift","generated_at":"2026-09-29T14:37:43.585858+00:00","license":"CC0-1.0","python":"3.12.14","seed":1,"split":"open-access"},"relevance":"Runs Python standard-library language operations in a deterministic local reproducer. Literal expected answers are authored independently. Related defects share an evaluation group to avoid benchmark split leakage.","root_cause":"Changes the omitted second-argument default. The executable reproducer isolates this operation from the rest of the contract.","sha256":"69bffb8d60b2c9f0fe2584557d162add8b65d4b402b66aaa69f5f44902eaab77","title":"Positional only binding: Changes the omitted second-argument default · case 01","variant":1,"variant_policy":"The five numbered cases rerun the same authored boundary fixtures; they are reproducibility runs, not independent input variants.","verified":true,"visibility":"public","verification":{"attempt":{"elapsed_ms":35.878,"exit_code":1,"observations":[{"actual":"TypeError","check":"keyword first rejected","expected":"TypeError","passed":true},{"actual":[1,10],"check":"omitted optional","expected":[1,10],"passed":true},{"actual":[1,2],"check":"two positions","expected":[1,2],"passed":true},{"actual":[1,3],"check":"named second","expected":[1,3],"passed":true},{"actual":[0,10],"check":"missing first","expected":"TypeError","passed":false},{"actual":"TypeError","check":"duplicate apparent first","expected":"TypeError","passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"keyword first rejected\", \"actual\": \"TypeError\", \"expected\": \"TypeError\", \"passed\": true}, {\"check\": \"omitted optional\", \"actual\": [1, 10], \"expected\": [1, 10], \"passed\": true}, {\"check\": \"two positions\", \"actual\": [1, 2], \"expected\": [1, 2], \"passed\": true}, {\"check\": \"named second\", \"actual\": [1, 3], \"expected\": [1, 3], \"passed\": true}, {\"check\": \"missing first\", \"actual\": [0, 10], \"expected\": \"TypeError\", \"passed\": false}, {\"check\": \"duplicate apparent first\", \"actual\": \"TypeError\", \"expected\": \"TypeError\", \"passed\": true}], \"passed\": false}\n"},"broken":{"elapsed_ms":108.11,"exit_code":1,"observations":[{"actual":"TypeError","check":"keyword first rejected","expected":"TypeError","passed":true},{"actual":[1,null],"check":"omitted optional","expected":[1,10],"passed":false},{"actual":[1,2],"check":"two positions","expected":[1,2],"passed":true},{"actual":[1,3],"check":"named second","expected":[1,3],"passed":true},{"actual":"TypeError","check":"missing first","expected":"TypeError","passed":true},{"actual":"TypeError","check":"duplicate apparent first","expected":"TypeError","passed":true}],"passed":false,"stderr":"","stdout":"{\"observations\": [{\"check\": \"keyword first rejected\", \"actual\": \"TypeError\", \"expected\": \"TypeError\", \"passed\": true}, {\"check\": \"omitted optional\", \"actual\": [1, null], \"expected\": [1, 10], \"passed\": false}, {\"check\": \"two positions\", \"actual\": [1, 2], \"expected\": [1, 2], \"passed\": true}, {\"check\": \"named second\", \"actual\": [1, 3], \"expected\": [1, 3], \"passed\": true}, {\"check\": \"missing first\", \"actual\": \"TypeError\", \"expected\": \"TypeError\", \"passed\": true}, {\"check\": \"duplicate apparent first\", \"actual\": \"TypeError\", \"expected\": \"TypeError\", \"passed\": true}], \"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."}}