--- name: python description: Write clean, readable Pythonic code. Use this skill any time you write or change a Python file. ---

# General guidelines

# Coding Style

- Always write clean, readable, well separated, well organized, Pythonic code. - Don't run linters or formatters, they will run automatically after every edit by the harness. - When using `datetime`, import it like this: `import datetime as dt` - CRITICAL: ALWAYS put ALL imports at the top of the file, NEVER inside functions, methods, or any other block. No exceptions. Use `TYPE_CHECKING` guard for type-only imports to avoid circular dependencies.

# Type hints

- ALWAYS type hint every function and method signature precisely even in tests. - NEVER write "-> None" type hint for return values, they are not necessary. - No need to type hint variables from functions call return values inside function bodies, they are inferred from the method return type, except extreme cases when the type is a huge help or a generic and it's concrete type cannot be determined. - Only use APIs, class names, variables or objects which you already read or know exist for sure. - Use the new pipe operator for `Optional` variables like this: `value | None` - Use `Any` for "all types" instead of `object`.

# Testing

- ALWAYS use `pytest` for all tests - ALWAYS assert on whole ouptut or full results in tests, not just tiny parts - For mocking, use pytest `monkeypatch` fixture, NEVER `unittest.mock` and NEVER any of the `Mock` classes or `patch` function - IMPORTANT: NEVER import from `conftest.py` - ALWAYS type hint test function parameters correctly. - Don't make a test class with only one function, a module-level test function is enough - NEVER use `unittest.mock` or any of the `Mock` classes or `patch` function, never assert on method calls, use real objects and assert on full results. When absolutely necessary and can't be avoided, use `pytest.monkeypatch`, when the test setup would be too difficult or the code have side effects, but consider writing a fake. - ALWAYS assert on the full result of the function call, never just list lengths or containment, except where that's the point.

# Managing dependencies

- Use `uv add` for adding dependencies, never directly edit `pyproject.toml` files. - For CLI scripts and apps, ALWAYS use `click` library instead of `argparse`, add it to dependencies if necessary.