error-handling-patterns

Error Handling Patterns

Build resilient applications with robust error handling strategies that gracefully handle failures and provide excellent debugging experiences.

When to Use This Skill

• Implementing error handling in new features
• Designing error-resilient APIs
• Debugging production issues
• Improving application reliability
• Creating better error messages for users and developers
• Implementing retry and circuit breaker patterns
• Handling async/concurrent errors
• Building fault-tolerant distributed systems

Core Concepts

1. Error Handling Philosophies

Exceptions vs Result Types:

• Exceptions: Traditional try-catch, disrupts control flow
• Result Types: Explicit success/failure, functional approach
• Error Codes: C-style, requires discipline
• Option/Maybe Types: For nullable values

When to Use Each:

• Exceptions: Unexpected errors, exceptional conditions
• Result Types: Expected errors, validation failures
• Panics/Crashes: Unrecoverable errors, programming bugs

2. Error Categories

Recoverable Errors:

• Network timeouts
• Missing files
• Invalid user input
• API rate limits

Unrecoverable Errors:

• Out of memory
• Stack overflow
• Programming bugs (null pointer, etc.)

Language-Specific Patterns

Python Error Handling

Custom Exception Hierarchy:

class ApplicationError(Exception):
    """Base exception for all application errors."""
    def __init__(self, message: str, code: str = None, details: dict = None):
        super().__init__(message)
        self.code = code
        self.details = details or {}
        self.timestamp = datetime.utcnow()

class ValidationError(ApplicationError):
    """Raised when validation fails."""
    pass

class NotFoundError(ApplicationError):
    """Raised when resource not found."""
    pass

class ExternalServiceError(ApplicationError):
    """Raised when external service fails."""
    def __init__(self, message: str, service: str, **kwargs):
        super().__init__(message, **kwargs)
        self.service = service

# Usage
def get_user(user_id: str) -> User:
    user = db.query(User).filter_by(id=user_id).first()
    if not user:
        raise NotFoundError(
            f"User not found",
            code="USER_NOT_FOUND",
            details={"user_id": user_id}
        )
    return user