rust-style-python Skill: Explicit, Typed Error Handling

Write Python the way Rust and Go are written: every failure path is explicit, typed, and handled at the intreturns an exit code, and the entry isif name == "main": raise SystemExit(main(sys.argv[1:]))`.

• main is the only place that maps Err to a log line and an exit code: 0 ok, 1 runtime error, 2 usage/validation error, 130 interrupted.
• One last-resort try/except BaseException in main logs the full traceback and returns nonzero. It is a safety net, never normal control flow.

10. Logging

• Structured logging (logging with extra= key/values, or structlog).
• Log each error once, at the boundary that handles it, not at every layer it passes through.
• No print for diagnostics.

11. Typing and Tooling

Full type hints everywhere, no Any unless justified in a comment. Code must pass mypy --strict (or pyright --strict) and ruff.

[tool.mypy]
strict = true
warn_unreachable = true

[tool.ruff]
target-version = "py312"

[tool.ruff.lint]
select = ["E", "F", "B", "BLE", "TRY", "ERA", "S", "SIM", "UP", "RET", "PL", "ANN"]

12. Tests

• pytest tests for every Err path, not just the happy path: malformed input, missing file, permission denied, timeout, partial failure, empty input, huge input, unicode edge cases.
• Use hypothesis for parsers and validators.

13. Output Format

Deliver in this order:

1. Failure-mode analysis (the pre-code table)
2. Error type definitions
3. Result/Option helpers (skip if using returns)
4. Boundary functions (I/O, parsing) returning Result
5. Pure core logic
6. main with exit-code mapping
7. pyproject.toml tooling config
8. Tests
9. A short failure-mode table: failure → error variant → how it's handled

14. Hard Constraints

• No try/except in core logic. It lives only in boundary functions and main.
• No exceptions for control flow.
• If a user requirement conflicts with these rules (for example, they want a quick sys.exit in the middle of a helper), point it out and propose the closest compliant alternative rather than silently breaking the rules.
• Match the scope to the task: a 30-line script still gets typed errors and a main with exit codes, but does not need an elaborate framework. Skip sections that genuinely don't apply (no concurrency means no concurrency section) and say so.