strict-python-mode

name	strict-python-mode
description	Enforces type hints, docstrings, and Python best practices. Use when writing or refactoring Python code, creating new functions, or when user mentions "production-ready" or "type-safe" code.
allowed-tools	Edit, Write, Read, Bash(ruff:*, mypy:*)

Strict Python Mode

Core Principles

When writing Python code in this project, ALWAYS follow these rules:

1. Type hints are mandatory

   • Every function parameter must have a type hint
   • Every function must have a return type annotation
   • Use from collections.abc import for generic types (list, dict, set)
   • Never use Any type - if type is unknown, use object or create proper Protocol

2. Docstrings are required

   • Every public function/method needs a docstring
   • Use Google-style docstrings format
   • Include Args, Returns, Raises sections

3. Modern Python syntax (3.12+)

   • Use list[str] instead of List[str] from typing
   • Use dict[str, int] instead of Dict[str, int]
   • Use X | None instead of Optional[X]
   • Use X | Y for Union types

Code Quality Checks

Before finishing ANY code changes, run these checks:

# 1. Format with Ruff
poetry run ruff format .

# 2. Lint with Ruff
poetry run ruff check . --fix

# 3. Type check with mypy (if available)
poetry run mypy app/ --ignore-missing-imports

Example: Good vs Bad

❌ Bad (will be rejected)

def get_user(id):
    user = db.get(id)
    return user

✅ Good (approved)

def get_user(user_id: int) -> User | None:
    """Fetch user by ID from database.
    
    Args:
        user_id: The unique identifier of the user
        
    Returns:
        User object if found, None otherwise
        
    Raises:
        DatabaseError: If database connection fails
    """
    user = db.get(user_id)
    return user

FastAPI-Specific Rules

Endpoint Signatures

# Always use dependency injection
@router.get("/users/{user_id}")
async def get_user(
    user_id: int,
    db: DatabaseSession = Depends(get_db),
    current_user: User = Depends(get_current_user),
) -> UserResponse:
    """Get user by ID."""
    ...

Response Models

# Always define explicit response models
class UserResponse(BaseModel):
    id: int
    username: str
    email: EmailStr
    created_at: datetime

    class Config:
        from_attributes = True

Validation Rules

Before ANY commit:

1. All new functions have type hints
2. All public functions have docstrings
3. Ruff format passes with no changes needed
4. Ruff check passes with no errors
5. If mypy is available, it passes with no errors

If any check fails, FIX IT before showing me the code.