FA-4426 / Mapping semantics / Open access

Map values retain duplicates · case 01

The operation returns a result or retained state that violates this contract: Return map values in key insertion order, retaining duplicate values.

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

ROOT CAUSE

Distinct-value conversion erases independent equal-valued bindings.

THE FAILURE

Distinct-value conversion erases independent equal-valued bindings.

Unsuccessful approach: Sorting keys replaces the required insertion order.

Case contract

Return map values in key insertion order, retaining duplicate values. 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

N = 1
observations = []
def solve(x, y=None):
    return list(dict.fromkeys(x.values()))
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('duplicate values', solve({'a': 'v', 'b': 'v'}), ['v', 'v'])
check('nonlexical keys', solve({'b': 'v', 'a': 'w'}), ['v', 'w'])
check('empty', solve({}), [])
check('None value', solve({'a': None}), [None])
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
duplicate values	`['v']`	`['v', 'v']`	Failed
nonlexical keys	`['v', 'w']`	`['v', 'w']`	Passed
empty	`[]`	`[]`	Passed
None value	`[None]`	`[None]`	Passed

SHA-256 / 29d39d91723b57435644fbab7744ea2698540d288f083ad3f4e94c7c5104892f

2 / The unsuccessful fix

Exit 1

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

N = 1
observations = []
def solve(x, y=None):
    return [x[k] for k in sorted(x)]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
check('duplicate values', solve({'a': 'v', 'b': 'v'}), ['v', 'v'])
check('nonlexical keys', solve({'b': 'v', 'a': 'w'}), ['v', 'w'])
check('empty', solve({}), [])
check('None value', solve({'a': None}), [None])
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
duplicate values	`['v', 'v']`	`['v', 'v']`	Passed
nonlexical keys	`['w', 'v']`	`['v', 'w']`	Failed
empty	`[]`	`[]`	Passed
None value	`[None]`	`[None]`	Passed

SHA-256 / 2b1c31db25a31fb5dcf95cf2739243d1e14a43ad804cec83dcadfb5d1f92c478

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.

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 2026-09-29T14:37:39.042384+00:00.

Case digest / 508a313233ffc933bef0e19e99786c920bac75e08de9f3d9e42bcbd8fb04a8d4