python

name	python
description	Always use this skill when writing or editing python code!

python

• Keep lines short.
• Use ruff for linting and formatting.
  • Install them with uv tool install ruff if not already installed.
• Never use "try ... except Exception" that swallows errors.
  • Prefer handling specific exceptions, logging, or re-raising it.
• Always add type hints to code; especially anything non-obvious.
  • Prefer | over Union[] and | None over Optional.
  • Run a type checker (pyright or whatever the project specifies) and fix all errors.
  • Prefer strict, tight type hints.
• Never import things from __future__, just use the latest Python features and require a modern Python version.
• Whenever possible, extract logic out to staticmethods and classmethods.
• Don't return multiline statements; prefer assigning then returning.
• Don't setup logging in libraries; leave that to the application using the library.
• Add doctests to regular expressions.

pydantic conventions

• Prefer the new validators over the older @validator decorators.
  • e.g.: number: Annotated[int, AfterValidator(is_even)]
• Prefer Annotated type aliases for constrained fields at module level for better reusability and readability.
• Prefer constrained types (e.g.: PositiveInt and EmailStr over bare int and str).

imports

• Imports should always be at the top of the file.
• Always use relative imports within a package (from ..schemas import ...).

dependencies

• Prefer adding dependencies without version constraints unless absolutely necessary.
• Never try except missing imports; assume users of our code will install all needed dependencies.
  • Add them to pyproject.toml, requirements.txt, or equivalent.
• When installing packages for source code that's local, use uv pip install -e ./path.
  • So we don't confuse ourselves editing local code and running things from site-packages.

naming

• UPPER_SNAKE_CASE for constants and regex patterns
• Module-level logger: log = logging.getLogger(__name__)

tests

• Rely on pytest.
  • Use markers effectively.
  • Tests are auto-marked unit unless explicitly @pytest.mark.integration.

negative examples

horizontal alignment is not pythonic

Never do this:

var1         = 1
my_other_var = 2

useless getters and setters

Always prefer accessing attributes directly over something like this:

  def get_my_items(self) -> list[MyItem]:
    return self.my_items