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.