Adversarial Python

Adversarial Python Gate

A modern-idiom and code-structure review gate for Python — pass/fail: a single blind reviewer subagent judges the work against this gate's rules with an adversarial mandate, and the work passes only when every rule is PASS or N/A. This skill renders verdicts; it never fixes the work.

The rules target two failure modes with one root cause — the author reproduced a shape instead of designing one. Training-data inertia produces code a modern Python feature deletes outright: the if/elif ladder that match or a registry replaces, the __init__/__repr__/__eq__ triple that @dataclass(slots=True) generates, the TypeVar ritual PEP 695 retired, the chunking helper itertools.batched shipped. Legacy-pattern propagation produces new code faithfully extending the surrounding codebase's bad structure — one more branch on the event ladder, one more method on the pass-through service — instead of tracing the feature end-to-end and modeling it. Each rule carries an Evidence of violation paragraph so a reviewer can decide PASS/FAIL/N/A from artifact evidence alone, and a Requires Python ≥ 3.X gate where the fix depends on a language version.

When to Apply

• A Python feature, endpoint, or module (agent-authored or human) is about to merge and needs an objective PASS/FAIL on whether modern Python and a fresh architectural look would delete or restructure it.
• An agent extended a legacy codebase and you suspect it copied the existing patterns — event/version branch ladders, service layers that only forward, stringly-typed state — instead of re-architecting the feature.
• A codebase raised its Python floor (to 3.12, 3.13, 3.14+) and changed code should be held to the idioms the new floor enables.
• A refactor claims to modernize or simplify and you want the claim verdict-checked rather than diff-skimmed.

Do not apply to targets with no Python source (the reviewer prompt's precondition aborts with "GATE NOT APPLICABLE"), or when the user wants explanations and refactors rather than a verdict. Judgment calls the gate deliberately excludes — naming taste, function length, docstring and test coverage, performance tuning — belong to advisory skills, not this gate.

Review Protocol

Follow these steps exactly — the gate's value is that every review runs the same way.

1. Identify the target. Pin down exactly what is under review (a diff, a set of files, a PR) and note the ref/paths so the review runs against an unambiguous, fixed target. Include the repo root — several alt- and disp- rules must search beyond the diff for implementers, substitution sites, test doubles, and call sites (the reviewer prompt lists them).
2. Probe the Python version. Read the target's Python floor from pyproject.toml (requires-python), .python-version, setup.cfg, or the CI matrix — cite the source; if undeclared, judge as the newest stable Python and say so. Then compare the floor against verified_python in metadata.json:
   • floor ≤ verified: proceed; version-gated rules above the floor will be N/A.
   • floor > verified: fetch https://docs.python.org/3/whatsnew/3.{N}.html for each version in the gap and compose a delta briefing — new stdlib batteries (they extend the std-no-hand-rolled-batteries table), new syntax and typing forms (they extend the disp-/typing- rules' reach), each line with its citation. The briefing goes into the reviewer prompt's {{VERSION_DELTA_BRIEFING}} slot. After the review, record the delta in gotchas.md so the rules can be re-verified and verified_python bumped.
3. Load the rules. Read references/_sections.md and every rule file in references/ (all disp-*.md, model-*.md, alt-*.md, typing-*.md, std-*.md, flow-*.md files).
4. Compose the reviewer prompt. Fill references/reviewer-prompt.md with the rules, the target, the Python floor, and the delta briefing (if any). The composed prompt must be fully self-contained — a reviewer sees no conversation history, so nothing may refer to context outside the prompt.
5. Dispatch one blind reviewer. Launch a single Task subagent whose entire input is the composed prompt — no conversation context, no commentary alongside it.
6. Render fail-closed. The reviewer's structured output is the verdict — there is no merge step. Overall verdict is PASS only when every rule is PASS or N/A; any single FAIL fails the gate. Never average, weigh severity, or waive a rule — a "minor" FAIL is a FAIL. If the reviewer returns "GATE NOT APPLICABLE" (no Python source in the target), stop and report that instead of a verdict.
7. Render the verdict. Fill assets/templates/verdict.md. On FAIL, aggregate the reviewer's "missing for PASS" suggestions into the fix list, each with its location, ordered by category importance. Every rule whose result is FAIL must appear in the fix list with a change concrete enough to apply as written — if the reviewer's suggestion only restates the violation, derive the fix from the rule's correct example before rendering.

If the same rule flips verdicts across re-reviews of an unchanged target, or a human reads the evidence and overrides the verdict, that is a decidability bug in the rule — record it in gotchas.md and sharpen the rule; do not override the gate.

Verdict Format

The reviewer returns, per rule: PASS | FAIL | N/A, evidence (file:line or a quote — required for PASS as well as FAIL), and for every FAIL, the fix that flips the rule to PASS once applied — the named change plus its location, never a restatement of the violation. The final report follows assets/templates/verdict.md.

Rule Categories

Gotchas

Read gotchas.md before dispatching the reviewer — it pre-records scope guards (the version probe's edge cases, shapes-not-brands, the diff-vs-repo search obligations, what "greenfield judgment" does and does not license) so the reviewer does not judge outside the rules.

Related Skills

• adversarial-ts-patterns — the TypeScript/React sibling gate for the same disease (over-abstraction and under-modeling); same protocol, different language.
• radical-simplification — the advisory sibling: cognitive moves for collapsing complexity when you want to fix a failed verdict, not judge it.

Reference Files