FA-4851 / Call argument binding / Open access

Positional only binding: Adds a default to the required first parameter · case 01

Adds a default to the required first parameter and changes the required Python-language result.

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

ROOT CAUSE

Adds a default to the required first parameter. The executable reproducer isolates this operation from the rest of the contract.

VERIFIED REPAIR

Call f(a, /, b=10) and return [a,b]. The first parameter is required and positional-only; b accepts position or keyword.

Unsuccessful approach: The alternative still fails because it accepts the positional-only parameter by keyword.

Case 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.

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=0, /, b=10):
        return [a,b]
    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('keyword first rejected', solve([], {'a': 1}), 'TypeError')
check('omitted optional', solve([1], {}), [1, 10])
check('two positions', solve([1, 2], {}), [1, 2])
check('named second', solve([1], {'b': 3}), [1, 3])
check('missing first', solve([], {}), 'TypeError')
check('duplicate apparent first', solve([1], {'a': 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
keyword first rejected	`TypeError`	`TypeError`	Passed
omitted optional	`[1, 10]`	`[1, 10]`	Passed
two positions	`[1, 2]`	`[1, 2]`	Passed
named second	`[1, 3]`	`[1, 3]`	Passed
missing first	`[0, 10]`	`TypeError`	Failed
duplicate apparent first	`TypeError`	`TypeError`	Passed

SHA-256 / fa0f1cbd4589c0595774fb459e67615b54d8660c49eeac9b9aaeeec8a557e370

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, b=10):
        return [a,b]
    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('keyword first rejected', solve([], {'a': 1}), 'TypeError')
check('omitted optional', solve([1], {}), [1, 10])
check('two positions', solve([1, 2], {}), [1, 2])
check('named second', solve([1], {'b': 3}), [1, 3])
check('missing first', solve([], {}), 'TypeError')
check('duplicate apparent first', solve([1], {'a': 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
keyword first rejected	`[1, 10]`	`TypeError`	Failed
omitted optional	`[1, 10]`	`[1, 10]`	Passed
two positions	`[1, 2]`	`[1, 2]`	Passed
named second	`[1, 3]`	`[1, 3]`	Passed
missing first	`TypeError`	`TypeError`	Passed
duplicate apparent first	`TypeError`	`TypeError`	Passed

SHA-256 / 67b55e228a296d33846c1ac5ce13e442155f6e59dcdf17dc0b2677403fe98aea

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(args, kwargs):
    def f(a, /, b=10):
        return [a,b]
    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('keyword first rejected', solve([], {'a': 1}), 'TypeError')
check('omitted optional', solve([1], {}), [1, 10])
check('two positions', solve([1, 2], {}), [1, 2])
check('named second', solve([1], {'b': 3}), [1, 3])
check('missing first', solve([], {}), 'TypeError')
check('duplicate apparent first', solve([1], {'a': 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
keyword first rejected	`TypeError`	`TypeError`	Passed
omitted optional	`[1, 10]`	`[1, 10]`	Passed
two positions	`[1, 2]`	`[1, 2]`	Passed
named second	`[1, 3]`	`[1, 3]`	Passed
missing first	`TypeError`	`TypeError`	Passed
duplicate apparent first	`TypeError`	`TypeError`	Passed

SHA-256 / a7f0c0db7e309a9433808a96015cde16baf5995584a62dbb286f89eaec3c823d

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 2026-09-29T14:37:43.585858+00:00.

Case digest / 3fa356406d58e58296978af100ef5a83fded22cc7f8ee0af00368b32791ad83b