Thalarch Python

Use the runtime, package manager, frameworks, typing policy, and quality tools already declared by the repository. Do not force uv, Poetry, Ruff, Pyright, FastAPI, Pydantic, or any other modern tool merely because it is popular.

Preflight

Identify:

• supported Python versions;
• pyproject.toml, setup/config files, lockfiles and environment manager;
• runtime/framework dependencies;
• formatter/linter/type checker configuration;
• test runner/plugins;
• packaging/distribution contract.

Use the repository's existing environment and commands when available.

Idiomatic Python

Prefer clear Python-native constructs:

• comprehensions/generator expressions for simple transformations;
• enumerate, zip, collections, itertools, pathlib, context managers, and other standard-library primitives where they clarify intent;
• dataclasses/value types when the repository and problem benefit from them;
• precise function/type contracts rather than type noise on obvious locals;
• EAFP only where the exception is the real boundary signal and failure cost is acceptable.

Do not compress complex business logic into clever expressions. A readable loop is better than a dense comprehension with hidden state or difficult branching.

Never use mutable default arguments unintentionally.

Typing

Follow the project's configured type checker and Python floor.

• Preserve generics and protocols where they encode useful contracts.
• Prefer unknown-equivalent narrowing via actual Python type guards/contracts rather than casual Any propagation.
• Do not add annotations unsupported by the repository's minimum runtime without the required compatibility mechanism.
• Treat runtime validation and static typing as separate concerns.

Async and concurrency

Identify whether the code uses asyncio, Trio/AnyIO, framework-managed async, threads, processes, or synchronous execution.

Review:

• blocking I/O inside the event loop;
• task ownership and cancellation;
• orphan/background task lifetime;
• timeout behavior;
• semaphore/queue backpressure;
• shared mutable state;
• CPU-bound work incorrectly placed in async tasks;
• resource cleanup during cancellation.

Do not introduce async merely to make code look modern. For CPU-bound work, profile and choose threads/processes/native/vectorized work based on the actual workload and GIL/runtime behavior.

Exceptions and resources

• Never use a bare except unless implementing a true process-level boundary where all failures must be captured and re-raised/reported deliberately.
• Catch specific exceptions you can handle or translate.
• Preserve traceback/cause when re-raising.
• Use context managers for owned files, locks, connections, transactions, and temporary resources.
• Do not convert failures to None, empty collections, or success responses unless that is the documented contract.

Web/API frameworks

Only use framework-specific patterns if the framework is present. Verify the installed version before writing decorators, dependency hooks, Pydantic model APIs, ORM calls, or lifecycle code.

For FastAPI/Django/Flask/other services, combine with thalarch-api, thalarch-security, and thalarch-data-sql when relevant.

Testing

Use the configured test stack. Strong evidence may include:

• focused pytest/unittest cases;
• parametrized boundary matrices;
• property-based tests when invariants matter and Hypothesis is available/justified;
• integration tests for DB/network/process boundaries;
• async tests using the repository's configured async plugin;
• regression tests that fail for the original bug.

Do not chase a coverage percentage independently of behavior risk.

Performance

Profile before tuning. Use available evidence such as cProfile, py-spy, scalene, tracemalloc, benchmark tooling, DB/query traces, or application metrics.

Look for algorithmic waste, repeated serialization/parsing, accidental materialization, N+1 I/O, event-loop blocking, excessive object churn, and unnecessary copies before reaching for native extensions or concurrency.

Verification

Run project-native format/lint/type/test/build/package commands as configured. State the actual Python version/environment used for version-sensitive claims.