FA-4916 / Call argument binding / Open access

Positional name in varkw: Allows the required positional value to be supplied through keyword rest · case 01

Allows the required positional value to be supplied through keyword rest and changes the required Python-language result.

Verified by executionVariant 1 · 5 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Allows the required positional value to be supplied through keyword rest. The executable reproducer isolates this operation from the rest of the contract.

THE FAILURE

Allows the required positional value to be supplied through keyword rest. The executable reproducer isolates this operation from the rest of the contract.

Unsuccessful approach: The alternative still fails because it accepts extra positional arguments despite having no variadic positional parameter.

Case contract

Call f(a, /, **rest), returning the positional a and the ordered [name,value] keyword pairs. A keyword named a belongs to rest. Inputs use the finite Python types shown in the fixtures. An error string denotes the specified caught exception, not an unhandled process failure.

Why this case matters

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.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(args, kwargs):
    def f(a=None, **rest):
        return [a,[[k,v] for k,v in rest.items()]]
    try:
        return f(*args, **kwargs)
    except TypeError:
        return "TypeError"
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('same spelling legal', solve([1], {'a': 2}), [1, [['a', 2]]])
check('ordered kwargs', solve([1], {'z': 0, 'a': 3, 'b': None}), [1, [['z', 0], ['a', 3], ['b', None]]])
check('no keywords', solve([None], {}), [None, []])
check('keyword cannot supply positional', solve([], {'a': 2}), 'TypeError')
check('too many positions', solve([1, 2], {}), 'TypeError')
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
same spelling legal	`TypeError`	`[1, [['a', 2]]]`	Failed
ordered kwargs	`TypeError`	`[1, [['z', 0], ['a', 3], ['b', None]]]`	Failed
no keywords	`[None, []]`	`[None, []]`	Passed
keyword cannot supply positional	`[2, []]`	`TypeError`	Failed
too many positions	`TypeError`	`TypeError`	Passed

SHA-256 / 17abc90bc48d877fb7a8abd6c5172f21896c4756ee7f3e0110a314daa026592e

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(args, kwargs):
    def f(a, /, *tail, **rest):
        return [a,[[k,v] for k,v in rest.items()]]
    try:
        return f(*args, **kwargs)
    except TypeError:
        return "TypeError"
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('same spelling legal', solve([1], {'a': 2}), [1, [['a', 2]]])
check('ordered kwargs', solve([1], {'z': 0, 'a': 3, 'b': None}), [1, [['z', 0], ['a', 3], ['b', None]]])
check('no keywords', solve([None], {}), [None, []])
check('keyword cannot supply positional', solve([], {'a': 2}), 'TypeError')
check('too many positions', solve([1, 2], {}), 'TypeError')
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
same spelling legal	`[1, [['a', 2]]]`	`[1, [['a', 2]]]`	Passed
ordered kwargs	`[1, [['z', 0], ['a', 3], ['b', None]]]`	`[1, [['z', 0], ['a', 3], ['b', None]]]`	Passed
no keywords	`[None, []]`	`[None, []]`	Passed
keyword cannot supply positional	`TypeError`	`TypeError`	Passed
too many positions	`[1, []]`	`TypeError`	Failed

SHA-256 / 156cc16bf75a989e435d0a68485851e75958f954bd76909d0f4fe8f568f9fcf9

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 5 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

Every case sharing this mechanism uses the same contract and the same repair, so this one record is held back for all of them.

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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 2026-09-29T14:37:44.323538+00:00.

Case digest / a1a0c5212ae2bc192e17360bfde8aa59f05fe5700f1ff3b856a30465a6a68cbf