FAILURE MAP
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FA-4971 / Descriptor lookup / Open access

Data descriptor storage: Returns an instance default for descriptor access on the class · case 01

Returns an instance default for descriptor access on the class and changes the required Python-language result.

Verified by executionVariant 1 · 4 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

Returns an instance default for descriptor access on the class. The executable reproducer isolates this operation from the rest of the contract.

THE FAILURE

Returns an instance default for descriptor access on the class. The executable reproducer isolates this operation from the rest of the contract.

Unsuccessful approach: The alternative still fails because it replaces a known zero backing value with the missing-value default.

Case contract

A data descriptor field takes precedence over an instance field shadow. Its backing key is _value, missing reads return 7, writes update that key, deletion removes it, and class access returns class-descriptor. Return [read results,final instance dictionary]. 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(initial, commands):
    class D:
        def __get__(self, obj, owner):
            if obj is None: return 7
            return obj.__dict__.get('_value',7)
        def __set__(self, obj, value):
            obj.__dict__['_value']=value
        def __delete__(self, obj):
            obj.__dict__.pop('_value',None)
    class C:
        field=D()
    c=C(); c.__dict__.update(initial); out=[]
    for op,value in commands:
        if op=='get': out.append(c.field)
        elif op=='class': out.append(C.field)
        elif op=='set': c.field=value
        elif op=='delete': del c.field
    return [out,dict(c.__dict__)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('descriptor beats shadow', solve({'field': 99, '_value': 2}, [['get', None], ['class', None]]), [[2, 'class-descriptor'], {'field': 99, '_value': 2}])
check('set and delete dispatch', solve({}, [['set', 5], ['get', None], ['delete', None], ['get', None]]), [[5, 7], {}])
check('zero is stored', solve({'_value': 0}, [['get', None]]), [[0], {'_value': 0}])
check('shadow survives descriptor delete', solve({'field': 4, '_value': 8}, [['delete', None], ['get', None]]), [[7], {'field': 4}])
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 fixtureActualExpectedOutcome
descriptor beats shadow[[2, 7], {'_value': 2, 'field': 99}][[2, 'class-descriptor'], {'_value': 2, 'field': 99}]Failed
set and delete dispatch[[5, 7], {}][[5, 7], {}]Passed
zero is stored[[0], {'_value': 0}][[0], {'_value': 0}]Passed
shadow survives descriptor delete[[7], {'field': 4}][[7], {'field': 4}]Passed

SHA-256 / 78f1b2a68748982adb640dd3aeb10f9d784dc697e0239f7efac5a3eead722a82

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json

N = 1
observations = []
def solve(initial, commands):
    class D:
        def __get__(self, obj, owner):
            if obj is None: return 'class-descriptor'
            return obj.__dict__.get('_value') or 7
        def __set__(self, obj, value):
            obj.__dict__['_value']=value
        def __delete__(self, obj):
            obj.__dict__.pop('_value',None)
    class C:
        field=D()
    c=C(); c.__dict__.update(initial); out=[]
    for op,value in commands:
        if op=='get': out.append(c.field)
        elif op=='class': out.append(C.field)
        elif op=='set': c.field=value
        elif op=='delete': del c.field
    return [out,dict(c.__dict__)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('descriptor beats shadow', solve({'field': 99, '_value': 2}, [['get', None], ['class', None]]), [[2, 'class-descriptor'], {'field': 99, '_value': 2}])
check('set and delete dispatch', solve({}, [['set', 5], ['get', None], ['delete', None], ['get', None]]), [[5, 7], {}])
check('zero is stored', solve({'_value': 0}, [['get', None]]), [[0], {'_value': 0}])
check('shadow survives descriptor delete', solve({'field': 4, '_value': 8}, [['delete', None], ['get', None]]), [[7], {'field': 4}])
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 fixtureActualExpectedOutcome
descriptor beats shadow[[2, 'class-descriptor'], {'_value': 2, 'field': 99}][[2, 'class-descriptor'], {'_value': 2, 'field': 99}]Passed
set and delete dispatch[[5, 7], {}][[5, 7], {}]Passed
zero is stored[[7], {'_value': 0}][[0], {'_value': 0}]Failed
shadow survives descriptor delete[[7], {'field': 4}][[7], {'field': 4}]Passed

SHA-256 / 56a0f5f4ac60e5fec262e4c16cab1058103bd9f5c8d26803d37a2817e204ef47

HELD IN THE MEMBER ARCHIVE

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

This mechanism has 4 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.

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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 2026-09-29T14:37:44.908717+00:00.

Case digest / 3185bb2603a4b8699dba4f0e5aeed669f1a9a259193cebc64507c4fa4a66e3eb