Python Core Idioms (3.12+)

When to use this skill

• Writing new Python code.
• Refactoring legacy Python scripts.
• Configuring linters (Ruff, MyPy).

1. Modern Syntax (3.10 – 3.12+)

• Type Hinting: Mandatory for function signatures. Use list[str], dict[str, int] (builtin generics) instead of List, Dict from typing.
• Union Types: Use str | None instead of Optional[str].
• Pattern Matching: Use match / case for complex control flow (structural pattern matching).
• Walrus Operator: Use := for assignment expression in if/while conditions when it improves readability (e.g., regex matching).
• f-strings: Use for all string interpolation.

2. Data Structures

• Dataclasses: Use @dataclass for data holding classes instead of strict dictionaries or raw classes.
  • frozen=True for immutability.
• TypedDict: For legacy JSON schemas where classes don’t fit.
• Enum: Inherit from StrEnum (3.11+) if string behavior is needed.

3. Project Structure

• pyproject.toml: Standard for configuration (ruff, pytest, mypy).
• Virtual Envs: Always use a venv or uv/poetry environment.