FA-4741 / Scoped mappings / Open access

Chainmap membership searches all scopes · case 01

The operation returns a result or retained state that violates this contract: Membership is true if any scope contains the key, regardless of its value.

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

ROOT CAUSE

Checking only the first scope misses inherited bindings.

VERIFIED REPAIR

Membership is true if any scope contains the key, regardless of its value.

Unsuccessful approach: Boolean lookup conflates absent keys with present falsy values.

Case contract

Membership is true if any scope contains the key, regardless of its value. Inputs are the finite Python values shown by the executable fixtures; no concurrent execution is assumed.

Why this case matters

A controlled local-runtime regression for collection APIs, language semantics, or ownership wrappers. Fixtures include boundary and interaction cases.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
from collections import Counter, ChainMap, deque
import heapq
N = 1
observations = []
def solve(x, y=None):
    return y in x[0]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('outer membership', solve([{}, {'a': 1}], 'a'), True)
check('None present', solve([{'a': None}], 'a'), True)
check('absent', solve([{}, {}], 'a'), False)
check('false present', solve([{}, {'a': False}], 'a'), True)
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
outer membership	`False`	`True`	Failed
None present	`True`	`True`	Passed
absent	`False`	`False`	Passed
false present	`False`	`True`	Failed

SHA-256 / 0e67638040ccd149cf1aa454963e2487735763ee6fe22a29dbb9ca663ba2bb39

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
from collections import Counter, ChainMap, deque
import heapq
N = 1
observations = []
def solve(x, y=None):
    return bool(ChainMap(*x).get(y))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('outer membership', solve([{}, {'a': 1}], 'a'), True)
check('None present', solve([{'a': None}], 'a'), True)
check('absent', solve([{}, {}], 'a'), False)
check('false present', solve([{}, {'a': False}], 'a'), True)
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
outer membership	`True`	`True`	Passed
None present	`False`	`True`	Failed
absent	`False`	`False`	Passed
false present	`False`	`True`	Failed

SHA-256 / f6c689c97cc6f4944368813e2883d553d8a9fe9967a5c925d11f707a150eb38f

3 / The verified repair

Exit 0

"""Failure Map reference implementation. Python standard library only."""
import json
from collections import Counter, ChainMap, deque
import heapq
N = 1
observations = []
def solve(x, y=None):
    return y in ChainMap(*x)
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('outer membership', solve([{}, {'a': 1}], 'a'), True)
check('None present', solve([{'a': None}], 'a'), True)
check('absent', solve([{}, {}], 'a'), False)
check('false present', solve([{}, {'a': False}], 'a'), True)
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
outer membership	`True`	`True`	Passed
None present	`True`	`True`	Passed
absent	`False`	`False`	Passed
false present	`True`	`True`	Passed

SHA-256 / 18129badb7c8c7eecf26a5e06d04d3fe9571ec4686616634b14361d56cfd41df

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 2026-09-29T14:37:42.187718+00:00.

Case digest / e6628dd933982999328e8b7f92e933dd7e24a58d943bb93b2e806dea03941a76