FA-5041 / Descriptor lookup / Open access

Descriptor owner argument: Reports a non-None instance during class descriptor access · case 01

Reports a non-None instance during class descriptor access and changes the required Python-language result.

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

ROOT CAUSE

Reports a non-None instance during class descriptor access. The executable reproducer isolates this operation from the rest of the contract.

VERIFIED REPAIR

Return [instance_is_None,owner_class_name] observed by an inherited descriptor for class, instance and super access. Owner is the accessing subclass, not necessarily the descriptor-defining class.

Unsuccessful approach: The alternative still fails because it drops instance binding for ordinary instance access.

Case contract

Return [instance_is_None,owner_class_name] observed by an inherited descriptor for class, instance and super access. Owner is the accessing subclass, not necessarily the descriptor-defining class. 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(mode):
    class D:
        def __get__(self,obj,owner): return [False,owner.__name__]
    class Base:
        field=D()
    class Child(Base): pass
    obj=Child()
    if mode=='base-class': return Base.field
    if mode=='child-class': return Child.field
    if mode=='instance': return obj.field
    if mode=='super': return super(Child,obj).field
    return Base().field
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('defining class access', solve('base-class'), [True, 'Base'])
check('inherited class access', solve('child-class'), [True, 'Child'])
check('subclass instance', solve('instance'), [False, 'Child'])
check('super keeps dynamic owner', solve('super'), [False, 'Child'])
check('base instance', solve('base-instance'), [False, 'Base'])
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
defining class access	`[False, 'Base']`	`[True, 'Base']`	Failed
inherited class access	`[False, 'Child']`	`[True, 'Child']`	Failed
subclass instance	`[False, 'Child']`	`[False, 'Child']`	Passed
super keeps dynamic owner	`[False, 'Child']`	`[False, 'Child']`	Passed
base instance	`[False, 'Base']`	`[False, 'Base']`	Passed

SHA-256 / 17955d980da0a4a22d1210055166f57c0a61f040eac08a49336e33ba56e7b5fb

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(mode):
    class D:
        def __get__(self,obj,owner): return [True,owner.__name__]
    class Base:
        field=D()
    class Child(Base): pass
    obj=Child()
    if mode=='base-class': return Base.field
    if mode=='child-class': return Child.field
    if mode=='instance': return obj.field
    if mode=='super': return super(Child,obj).field
    return Base().field
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('defining class access', solve('base-class'), [True, 'Base'])
check('inherited class access', solve('child-class'), [True, 'Child'])
check('subclass instance', solve('instance'), [False, 'Child'])
check('super keeps dynamic owner', solve('super'), [False, 'Child'])
check('base instance', solve('base-instance'), [False, 'Base'])
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
defining class access	`[True, 'Base']`	`[True, 'Base']`	Passed
inherited class access	`[True, 'Child']`	`[True, 'Child']`	Passed
subclass instance	`[True, 'Child']`	`[False, 'Child']`	Failed
super keeps dynamic owner	`[True, 'Child']`	`[False, 'Child']`	Failed
base instance	`[True, 'Base']`	`[False, 'Base']`	Failed

SHA-256 / 33b89edaae709b1b4cf6bf04d626e58e65ab92fbfc089c3bc0c86f7511182ba3

3 / The verified repair

Exit 0

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

N = 1
observations = []
def solve(mode):
    class D:
        def __get__(self,obj,owner): return [obj is None,owner.__name__]
    class Base:
        field=D()
    class Child(Base): pass
    obj=Child()
    if mode=='base-class': return Base.field
    if mode=='child-class': return Child.field
    if mode=='instance': return obj.field
    if mode=='super': return super(Child,obj).field
    return Base().field
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('defining class access', solve('base-class'), [True, 'Base'])
check('inherited class access', solve('child-class'), [True, 'Child'])
check('subclass instance', solve('instance'), [False, 'Child'])
check('super keeps dynamic owner', solve('super'), [False, 'Child'])
check('base instance', solve('base-instance'), [False, 'Base'])
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
defining class access	`[True, 'Base']`	`[True, 'Base']`	Passed
inherited class access	`[True, 'Child']`	`[True, 'Child']`	Passed
subclass instance	`[False, 'Child']`	`[False, 'Child']`	Passed
super keeps dynamic owner	`[False, 'Child']`	`[False, 'Child']`	Passed
base instance	`[False, 'Base']`	`[False, 'Base']`	Passed

SHA-256 / e13764a3905a1d701f986a8f8b660fd6ecaedf7105c7bc355bf253b524f5e66c

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 2026-09-29T14:37:45.623816+00:00.

Case digest / ddcad1dfe0ec3052fa3dc5c60068bff27870c4305176a5eca4d2f48b25e4ed54