🛡️ Error Handling Skill

Context

An application "functioning to perfection" means it NEVER crashes unconditionally. It manages errors gracefully.

1. Hierarchy of Exceptions

Define custom exceptions in src/core/exceptions.py.

python

class AppError(Exception):
    """Base class for all application errors."""
    pass

class ServiceError(AppError):
    """Errors in the service layer."""
    pass

class UIError(AppError):
    """Errors in the UI layer."""
    pass

2. The Safe UI Decorator

NEVER let an exception crash the GUI thread. Use a decorator for event handlers.

python

import functools
import wxcustom  # Hypothetical util
from src.core.logging import get_logger

logger = get_logger(__name__)

def safe_event(func):
    """Swallows exceptions and shows an Error Dialog."""
    @functools.wraps(func)
    def wrapper(self, *args, **kwargs):
        try:
            return func(self, *args, **kwargs)
        except Exception as e:
            logger.exception("Uncaught UI Error")
            wx.MessageBox(f"An unexpected error occurred: {e}", "Error", wx.ICON_ERROR)
    return wrapper

3. Boundary Pattern

Service layers should catch low-level exceptions (e.g., requests.exceptions.ConnectionError) and re-raise them as domain exceptions (NetworkError), preserving the stack trace (raise ... from e).

python

def fetch_data():
    try:
        http_client.get(...)
    except RequestException as e:
        logger.error("Failed to fetch data")
        raise ServiceError("Could not retrieve data") from e

4. Checklist

• Are UI event handlers decorated/protected?
• Are we using logger.exception() in catch blocks?
• Are we re-raising with context (from e)?