FA-4901 / Call argument binding / Open access

Variadic positional binding: Copies a named flag into the positional tail · case 01

Copies a named flag into the positional tail and changes the required Python-language result.

Verified by executionVariant 1 · 6 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Copies a named flag into the positional tail. The executable reproducer isolates this operation from the rest of the contract.

THE FAILURE

Copies a named flag into the positional tail. The executable reproducer isolates this operation from the rest of the contract.

Unsuccessful approach: The alternative still fails because it consumes the first variadic positional argument as flag.

Case contract

Call f(a, *tail, flag=False), returning [a,list(tail),flag]. flag must be named; arbitrary extra positions belong to tail. 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, *tail, flag=False):
        return [a,list(tail)+([flag] if flag is not False else []),flag]
    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('only required', solve([1], {}), [1, [], False])
check('several extras', solve([1, 2, 3], {}), [1, [2, 3], False])
check('named flag', solve([1, 2], {'flag': True}), [1, [2], True])
check('nested tail preserved', solve([1, [2, 3]], {}), [1, [[2, 3]], False])
check('unknown keyword', solve([1], {'other': 2}), 'TypeError')
check('missing required', solve([], {}), '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
only required	`[1, [], False]`	`[1, [], False]`	Passed
several extras	`[1, [2, 3], False]`	`[1, [2, 3], False]`	Passed
named flag	`[1, [2, True], True]`	`[1, [2], True]`	Failed
nested tail preserved	`[1, [[2, 3]], False]`	`[1, [[2, 3]], False]`	Passed
unknown keyword	`TypeError`	`TypeError`	Passed
missing required	`TypeError`	`TypeError`	Passed

SHA-256 / 2c35d383c290f5eb2d51e6880fcb0c06f1881f78f523096577f1430bb0bdd66c

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, flag=False, *tail):
        return [a,list(tail),flag]
    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('only required', solve([1], {}), [1, [], False])
check('several extras', solve([1, 2, 3], {}), [1, [2, 3], False])
check('named flag', solve([1, 2], {'flag': True}), [1, [2], True])
check('nested tail preserved', solve([1, [2, 3]], {}), [1, [[2, 3]], False])
check('unknown keyword', solve([1], {'other': 2}), 'TypeError')
check('missing required', solve([], {}), '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
only required	`[1, [], False]`	`[1, [], False]`	Passed
several extras	`[1, [3], 2]`	`[1, [2, 3], False]`	Failed
named flag	`TypeError`	`[1, [2], True]`	Failed
nested tail preserved	`[1, [], [2, 3]]`	`[1, [[2, 3]], False]`	Failed
unknown keyword	`TypeError`	`TypeError`	Passed
missing required	`TypeError`	`TypeError`	Passed

SHA-256 / 40dcf99e2ad0d2e2f3f588c95cd5d2401cf3338741905a4ac6e90700b04b3b25

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 6 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.

Member access is invitation-based. Sign in with your invited account to inspect the repair.

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 2026-09-29T14:37:44.082047+00:00.

Case digest / 95cc01a4e8791e618250a472987945199a2f8529932aca652f6801eaf625952a